feat(docs): add note to docs about CI issues

Signed-off-by: vados <[email protected]>

docs/ci.md

@@ -9,3 +9,19 @@ To push up images that are used from continuous integration:
    2. Automatically, via `just docker-login` which will use the `git-crypt` protected credentials (you must have run `git-crypt` unlock first)
 4. Observe the docker login credentials generated in this local repo directory (`secrets/docker/config.json`)
 5. Run `just build-ci-image push-ci-image`
+
+## FAQ
+
+Issues that come up during FAQ
+
+### Old/outdated `cargo-pgrx` versions during CI runs
+
+If you find a CI run failing due to an unexpectedly outdated version of `cargo-pgrx`, try the following:
+
+- Ensure relevant builder Dockerfiles are up to date (ex. [`infra/docker/builder-gnu.Dockerfile`](../infra/docker/builder-gnu.Dockerfile))
+- Ensure relevant base Dockerfiles are up to date (ex. [`infra/docker/base-pkg-alpine3.20.3-amd64.Dockerfile`](../infra/docker/base-pkg-alpine3.20.3-amd64.Dockerfile))
+- Clear CI build caches (via online GUI)
+
+> ![NOTE]
+> See [the `Justfile`](../Justfile) for easy-to-run targets that build and push
+> the images mentioned above (ex. `just build-builder-image`)