fix(ci): exclude upstream rusty_v8 checkout from clean-worktree gate

The v8-canary windows-source job checks out denoland/rusty_v8 into
upstream-rusty-v8/ inside the workspace, so the final check-clean-worktree
step always flags it as untracked and fails the job after the artifacts
were built, staged, smoke-linked and uploaded successfully. Exclude the
directory in .gitignore: the checkout is intentional, not debris.

Author: KooshaPari

.gitignore

@@ -8,6 +8,11 @@ bazel-*
 build/
 out/
 
+# CI: upstream rusty_v8 checkout used by the v8-canary windows-source job.
+# The workflow checks this repo out into the workspace, so exclude it from
+# the check-clean-worktree gate (the checkout is intentional, not debris).
+/upstream-rusty-v8/
+
 # Node.js
 node_modules/
 .pnpm-store/