workflows: Add format check

Now that we have formatted tree-wide, use meson's clang-format-check
target to ensure no format regressions.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>

Author: jk-ozlabs

.github/workflows/pr.yml

@@ -23,5 +23,8 @@ jobs:
       - name: Build mctp
         run: meson compile -C build
 
+      - name: Check formatting
+        run: ninja -C build clang-format-check
+
       - name: Test mctp
         run: meson test -C build