LibCore: Remove unnecessary lifetime extension from ProcessSpawnOptions

We don't need `file_actions` to be a constant-reference. It's created
in-place by its one user (HackStudio). Because it is currently a const-
ref, if we try to create a ProcessSpawnOptions like so:

    Core::ProcessSpawnOptions options { .name = "foo"sv };

We get the following error with clang 18:

    lifetime extension of temporary created by aggregate initialization
    using a default member initializer is not yet supported; lifetime of
    temporary will end at the end of the full-expression

Userland/Libraries/LibCore/Process.h

@@ -41,7 +41,7 @@ struct ProcessSpawnOptions {
     Optional<ByteString> working_directory {};
 
     using FileActionType = Variant<FileAction::OpenFile, FileAction::CloseFile>;
-    Vector<FileActionType> const& file_actions {};
+    Vector<FileActionType> file_actions {};
 };
 
 class IPCProcess;