Enact some security improvements that I'd missed in previous rounds.

For each project, that includes some subset of:

- `zizmor` fixes (this time for [excessive permissions](https://docs.zizmor.sh/audits/#excessive-permissions)): compare 754877f (or cl/957369925 for excessive permissions specifically)
- migration off `styfle/cancel-workflow-action` (which requires write permissions): compare 68ac320
  - Relatedly, set up cancellation for bazel_common using the replacement we're using elsewhere (`concurrency`), since bazel_common didn't have cancellation set up at all yet.
- Dependabot `cooldown`: compare 9854090

RELNOTES=n/a
PiperOrigin-RevId: 958410064

Author: cpovirk

.github/workflows/ci.yml

@@ -13,6 +13,9 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
+permissions:
+  contents: read
+
 jobs:
   test:
     name: "JDK ${{ matrix.java }}"