ci: switch CentOS 7 test to Cirrus CI

On Cirrus CI we can run tests on the orignal CentOS 7 kernel.

The kernel is rather old, but on GitHub Actions we a 5.8 kernel
and a containerized CentOS 7 user space not much is working
correctly anymore. With this commit CentOS 7 based tests are
no longer running on GitHub Actions but on Cirrus CI.

Signed-off-by: Adrian Reber <areber@redhat.com>

.github/workflows/centos-test.yml

@@ -1,15 +0,0 @@
-name: CentOS Test
-
-on: [push, pull_request]
-
-jobs:
-  build:
-    runs-on: ubuntu-20.04
-    strategy:
-      matrix:
-        target: [centos7]
-
-    steps:
-    - uses: actions/checkout@v2
-    - name: Run CentOS ${{ matrix.target }} Test
-      run: sudo -E make -C scripts/ci ${{ matrix.target }}