Run min test in PR CI workflow

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

.github/workflows/ci-pr.yaml

@@ -20,7 +20,7 @@ jobs:
         uses: frequenz-floss/[email protected]
         with:
           python-version: "3.11"
-          nox-session: ci_checks_max
+          nox-session: ci_checks_min
 
   test-docs:
     name: Test documentation website generation

.github/workflows/ci.yaml

@@ -1,7 +1,6 @@
 name: CI
 
 on:
-  pull_request:
   merge_group:
   push:
     # We need to explicitly include tags because otherwise when adding