CI: Move Windows CI to a separate workflow

Having the pull_request 'labeled' event trigger the main CI is much too
impactful, since it cancels running jobs and does not start anything if
the label is anything else than 'windows'. Let's go with a different
approach and put the Windows CI job in a separate workflow.

How this works:

  * Jobs are only run if the 'windows' label is present on the PR.
  * If a PR is opened or updated, existing jobs are canceled.
  * If a PR is (un)labeled, existing jobs are only canceled if the label
    was 'windows'. Other labels cause the job to be rescheduled.

As far as I can see, there's no way to prevent the job from being
rescheduled when labels other than 'windows' are being added or removed.
However, by not canceling the existing Windows job, we can try to create
a cache so the next run will be much quicker.

.github/workflows/ci-windows.yml

@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - labeled
+      - unlabeled
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  # Do not cancel in-progress runs if a labeling action took place (other than 'windows'). Otherwise, adding irrelevant
+  # labels causes existing runs to be canceled and a new (identical) run to be started.
+  cancel-in-progress: ${{ (github.event.action != 'labeled' && github.event.action != 'unlabeled') || github.event.label.name == 'windows' }}
+
+jobs:
+  CI:
+    # Only run this job if the PR has the 'windows' label.
+    if: |
+      github.repository == 'LadybirdBrowser/ladybird'
+      && contains(github.event.pull_request.labels.*.name, 'windows')
+    name: 'Windows, x86_64, Windows_SanitizerCI, ClangCL'
+    uses: ./.github/workflows/lagom-template.yml
+    with:
+      toolchain: 'ClangCL'
+      os_name: 'Windows'
+      runner_labels: '["windows-2025"]'
+      arch: 'x86_64'
+      build_preset: 'Windows_Sanitizer_CI'
+      clang_plugins: false

.github/workflows/ci.yml

@@ -1,13 +1,6 @@
 name: CI
 
-on:
-  push:
-  pull_request:
-    types:
-      - opened
-      - synchronize
-      - reopened
-      - labeled
+on: [push, pull_request]
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || format('{0}-{1}', github.ref, github.run_number) }}
@@ -16,12 +9,7 @@ concurrency:
 jobs:
   # CI matrix - runs the job in lagom-template.yml with different configurations.
   Lagom:
-    # Run the items in this matrix only if:
-    # 1. The repository is the Ladybird repository; and
-    # 2. If the event was a push event, or a PR event other than 'labeled', or the label name is 'windows'
-    if: |
-      github.repository == 'LadybirdBrowser/ladybird'
-      && (github.event_name != 'pull_request' || github.event.action != 'labeled' || github.event.label.name == 'windows')
+    if: github.repository == 'LadybirdBrowser/ladybird'
     name: ${{ matrix.os_name }}, ${{ matrix.arch }}, ${{ matrix.build_preset }}, ${{ matrix.toolchain }}
 
     strategy:
@@ -33,7 +21,6 @@ jobs:
         toolchain: ['GNU']
         clang_plugins: [false]
         runner_labels: ['["blacksmith-16vcpu-ubuntu-2404"]']
-        enabled: [true]
 
         include:
           - os_name: 'Linux'
@@ -42,7 +29,6 @@ jobs:
             toolchain: 'Clang'
             clang_plugins: true
             runner_labels: '["blacksmith-16vcpu-ubuntu-2404"]'
-            enabled: true
 
           - os_name: 'macOS'
             arch: 'arm64'
@@ -50,7 +36,6 @@ jobs:
             toolchain: 'Clang'
             clang_plugins: false
             runner_labels: '["macos-15", "self-hosted"]'
-            enabled: true
 
           - os_name: 'Linux'
             arch: 'x86_64'
@@ -58,15 +43,6 @@ jobs:
             toolchain: 'Clang'
             clang_plugins: false
             runner_labels: '["blacksmith-16vcpu-ubuntu-2404"]'
-            enabled: true
-
-          - os_name: 'Windows'
-            arch: 'x86_64'
-            build_preset: 'Windows_Sanitizer_CI'
-            toolchain: 'ClangCL'
-            clang_plugins: false
-            runner_labels: '["windows-2025"]'
-            enabled: ${{ contains(github.event.pull_request.labels.*.name, 'windows') }}
 
     uses: ./.github/workflows/lagom-template.yml
     with:
@@ -76,4 +52,3 @@ jobs:
       arch: ${{ matrix.arch }}
       build_preset: ${{ matrix.build_preset }}
       clang_plugins: ${{ matrix.clang_plugins }}
-      enabled: ${{ matrix.enabled }}

.github/workflows/lagom-template.yml

@@ -22,10 +22,6 @@ on:
         required: false
         type: boolean
         default: false
-      enabled:
-        required: false
-        type: boolean
-        default: true
 
 env:
   # runner.workspace = /home/runner/work/ladybird
@@ -42,7 +38,6 @@ env:
 
 jobs:
   CI:
-    if: ${{ inputs.enabled }}
     runs-on: ${{ fromJSON(inputs.runner_labels) }}
 
     steps: