Devops: Loosen trigger conditions for Docker build CI workflow (#6131)

The docker build workflow was only activated when changes were made to
either the `.docker` directory or `.github/workflows/docker*.yaml` files.
However, changes in the `aiida` package could also break the build and
so could pass by unnoticed.

The trigger conditions are changed to instead trigger always except for
changes to the `tests` and `docs` directories.

Cherry-pick: 1b5b669

.github/workflows/docker.yml

@@ -3,17 +3,17 @@ name: Build, test and push Docker Images
 
 on:
     pull_request:
-        paths:
-            - .docker/**
-            - .github/workflows/docker-*.yml
+        paths-ignore:
+            - "docs/**"
+            - "tests/**"
     push:
         branches:
             - main
         tags:
             - "v*"
-        paths:
-            - .docker/**
-            - .github/workflows/docker-*.yml
+        paths-ignore:
+            - "docs/**"
+            - "tests/**"
     workflow_dispatch:
 
 # https://docs.github.com/en/actions/using-jobs/using-concurrency