[Infra] Show diff colours

Show colours for `git diff` in CI to make them easier to read for those who can see red-green colours.

Author: martincostello

.github/workflows/build.yml

@@ -132,5 +132,6 @@ jobs:
         shell: bash
         run: |
           git status
-          git diff
+          git config color.diff always
+          git --no-pager diff
           [[ -z "$(git status --porcelain)" ]]