workflows: exclude ubuntu-latest from beam_PostCommit_Python

Author: mohamedawnallah

.github/workflows/beam_PostCommit_Python.yml

@@ -62,12 +62,7 @@ jobs:
         job_name: ['beam_PostCommit_Python']
         job_phrase: ['Run Python PostCommit']
         python_version: ['3.9', '3.10', '3.11', '3.12']
-        # Run on both self-hosted and GitHub-hosted runners.
-        # Some tests (marked require_docker_in_docker) can't run on Beam's
-        # self-hosted runners due to Docker-in-Docker environment constraint.
-        # These tests will only execute on ubuntu-latest (GitHub-hosted).
-        # Context: https://github.com/apache/beam/pull/35585.
-        os: [[self-hosted, ubuntu-20.04, highmem22], [ubuntu-latest]]
+        os: [[self-hosted, ubuntu-20.04, highmem22]]
     if: |
       github.event_name == 'workflow_dispatch' ||
       github.event_name == 'pull_request_target' ||
@@ -105,11 +100,7 @@ jobs:
           arguments: |
             -Pjava21Home=$JAVA_HOME_21_X64 \
             -PuseWheelDistribution \
-            -Pposargs="${{
-              contains(matrix.os, 'self-hosted') &&
-                '-m (not require_docker_in_docker)' ||
-                '-m require_docker_in_docker'
-            }}" \
+            -Pposargs="-m (not require_docker_in_docker)" \
             -PpythonVersion=${{ matrix.python_version }} \
         env:
           CLOUDSDK_CONFIG: ${{ env.KUBELET_GCLOUD_CONFIG_PATH}}