ci: check 'update-man-rules' to ensure it is not forgotten

We often forget to run this command when updating manpages, and notice
only much later. Add a step in the CI to flag it, as we already do for
the D-Bus docs.

(cherry picked from commit 1219b0e816)
(cherry picked from commit 72cb20049e)
(cherry picked from commit 69dd7dac89)
(cherry picked from commit 77ec86e0a9)

.github/workflows/linter.yml

@@ -79,3 +79,8 @@ jobs:
 
       - name: Run clang-tidy
         run: mkosi box -- meson test -C build --suite=clang-tidy --print-errorlogs --no-stdsplit
+
+      - name: Run man-rules checks
+        run: |
+          mkosi box -- ninja -C build update-man-rules
+          git diff --exit-code -- man/rules/meson.build