ci: disable Windows on PRs (#12162)

With merge queues we don't need to run all tests on Windows in CI
on every PR update, since any failure will still block merging.

Author: DaniPopes

.github/scripts/matrices.py

@@ -75,11 +75,7 @@ def __init__(
 )
 t_macos = Target("depot-macos-latest", "aarch64-apple-darwin", "macosx-aarch64")
 t_windows = Target("depot-windows-latest-16", "x86_64-pc-windows-msvc", "windows-amd64")
-targets = (
-    [t_linux_x86, t_windows]
-    if is_pr
-    else [t_linux_x86, t_linux_arm, t_macos, t_windows]
-)
+targets = [t_linux_x86] if is_pr else [t_linux_x86, t_linux_arm, t_macos, t_windows]
 
 config = [
     Case(