fix and reenable CodeQL

[vchudnov-g]

CodeQL was consistently running out of disk space, which was causing errors and blocking PRs, so I disabled it.

We need to fix the underlying issue (possibly by configuring larger runners at the org level; see https://docs.github.com/en/code-security/code-scanning/troubleshooting-code-scanning/out-of-disk-or-memory) and re-enable CodeQL since it provides security checks.

[vchudnov-g]

Googlers: b/360135010 to track a possible org-wide solution, which would unblock reenabling CodeQL in this repo.

[parthea]

Closing as duplicate of the org-wide issue b/360135010