ci: List Godot versions to test one per line

This will make future diffs that add and remove engine versions more
legible.

Author: wjt

.github/workflows/checks.yaml

@@ -27,7 +27,9 @@ jobs:
     name: Tests
     strategy:
       matrix:
-        godot-version: [4.2.2, 4.3.0]
+        godot-version:
+          - 4.2.2
+          - 4.3.0
     runs-on: ubuntu-latest
     steps:
     - name: Checkout