Disable weekly CI jobs in forks (#455)

### Proposed changes

It has been recently brought to my attention that our weekly CI jobs are
getting run in fork repositories. Users may inadvertently end up in this
scenario if they enable GHA workflows on their forks, see
https://github.com/orgs/community/discussions/26704.

While I do think it makes sense for plain CI jobs to be available to
forks if the owners chooses to, weekly CI jobs seem like a waste of
compute. This patch ensures those jobs only run for this repository.

#### Type of change

- [x] 🐛 Bugfix (change which fixes an issue)
- [ ] 🚀 Feature (change which adds functionality)
- [ ] 📚 Documentation (change which fixes or extends documentation)

### Checklist

- [x] Lint and unit tests (if any) pass locally with my changes
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] I have added necessary documentation (if appropriate)
- [x] All commits have been signed for
[DCO](https://developercertificate.org/)

Signed-off-by: Michel Hidalgo <[email protected]>

.github/workflows/docker_ci_pipeline.yml

@@ -16,6 +16,7 @@ on:
 
 jobs:
   build-image:
+    if: github.repository == 'Ekumen-OS/beluga'
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false

.github/workflows/weekly_pipeline.yml

@@ -16,6 +16,7 @@ concurrency:
 
 jobs:
   build-test:
+    if: github.repository == 'Ekumen-OS/beluga'
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false