PGO update: Parse flags more correctly.

There is already a loop parsing the `--tolerate-no-profile-changes` flag.
Use it.

Without this CL, the `git status` command actually always runs, because
the `shift` in the earlier loop hides the argument from its view of `"$@"`.

PiperOrigin-RevId: 775426052

Author: EtiennePerot

.buildkite/scripts/pgo/maybe-skip.sh

@@ -52,7 +52,7 @@ if [[ "$(gh pr --repo="$repo_url" list --label pgo-update --state open --json ti
   exit 0
 fi
 
-if ! echo "$@" | grep -qFe '--tolerate-no-profile-changes'; then
+if [[ "$tolerate_no_profile_changes" == false ]]; then
   if [[ "$(git status --porcelain runsc/profiles | wc -l)" == 0 ]]; then
     echo "No changes to runsc profiles; skipping." >&2
     exit 0