CI: Github Actions scan failing (zizmor-output)

[lanctot]

https://github.com/google-deepmind/open_spiel/actions/runs/33344080085/job/99344887601?pr=1599

[lanctot]

Run trap 'if [ "$?" -ne 0 ]; then echo ""; echo "For Googlers: Refer to go/github-zizmor-help for internal guidance on resolving issues."; fi' EXIT
Mandatory checks to evaluate: ["bot-conditions","insecure-commands","known-vulnerable-actions","template-injection","unpinned-uses","unredacted-secrets","unsound-condition"]
Zizmor format github exit code: 14
Error: Found 3 findings for mandatory checks that must always succeed.
Error: unpinned action reference: action is not pinned to a hash (required by blanket policy)
Error: unpinned action reference: action is not pinned to a hash (required by blanket policy)
Error: unpinned action reference: action is not pinned to a hash (required by blanket policy)
=========================================
CRITICAL: The following mandatory checks failed:
- zizmor/unpinned-uses at line 81 of .github/workflows/actions.yml: unpinned action reference: action is not pinned to a hash (required by blanket policy)
- zizmor/unpinned-uses at line 84 of .github/workflows/actions.yml: unpinned action reference: action is not pinned to a hash (required by blanket policy)
- zizmor/unpinned-uses at line 89 of .github/workflows/actions.yml: unpinned action reference: action is not pinned to a hash (required by blanket policy)
=========================================
Failing due to zizmor finding severity of Medium/High (exit code: 14).

See https://docs.zizmor.sh/audits/ for more info about these checks.
See https://docs.zizmor.sh/usage/#ignoring-results for ignoring checks that are false positive.

For Googlers: Refer to go/github-zizmor-help for internal guidance on resolving issues.
Error: Process completed with exit code 1.