Fix doc builder image version checks on forks

### Brief summary of bug

The ["Build and test ctsm-docs container" workflow](https://github.com/ESCOMP/CTSM/blob/1fc4af42654a1d4bca1380c616ad5b68f9d6412a/.github/workflows/docker-image-build.yml) can fail when run on forks: for example, [this run](https://github.com/adrifoster/CTSM/actions/runs/24679394282/job/72172444038#step:3:29) on @adrifoster's fork. Specifically, it tries to check the manifest for the ctsm-docs container under the forker's username rather than ESCOMP. Instead, it should always check against ESCOMP.

Also should probably prevent the "and publish" workflow from triggering at all on forks.

### General bug information

**CTSM version you are using:** ctsm5.4.034

**Does this bug cause significantly incorrect results in the model's science?** No

**Configurations affected:** n/a