ci: Reland run devtools tests whenever we run unit tests from #38614 (#39267)

This patch updates `linux.yml`, `mac.yml`, and `windows.yml` to run the
devtools test suite (https://github.com/servo/servo/issues/36325).


Testing: this patch effectively adds all devtools tests to CI
Fixes: https://github.com/servo/servo/issues/36325

Signed-off-by: atbrakhi <atbrakhi@igalia.com>
Co-authored-by: Delan Azabani <dazabani@igalia.com>

.github/workflows/linux.yml

@@ -194,6 +194,9 @@ jobs:
           timeout_minutes: 20
           max_attempts: 2 # https://github.com/servo/servo/issues/30683
           command: ./mach test-unit --${{ inputs.profile }}
+      - name: Devtools tests
+        if: ${{ inputs.unit-tests }}
+        run: ./mach test-devtools --${{ inputs.profile }}
       - name: Archive build timing
         uses: actions/upload-artifact@v4
         with: