CI: Allow run step of on target tests to fail

As documented in SerenityOS#5541, there are some Kernel issues that can
sporadically cause the test run to fail. Add continue on error with a
loud comment to let readers know what the issue(s) might be.

.github/workflows/cmake.yml

@@ -110,6 +110,8 @@ jobs:
  SERENITY_RUN: "ci"
  run: ninja run
  timeout-minutes: 10
+ # FIXME: When stable, remove continue on error. (See issue #5541)
+ continue-on-error: true
  - name: Print target logs
  if: ${{ !cancelled() && matrix.debug-macros == 'NORMAL_DEBUG'}}
  working-directory: ${{ github.workspace }}/Build