CI: Split pytest build system tests into parallel jobs

.gitlab/ci/build.yml

@@ -773,6 +773,7 @@ test_build_system_spaces:
 
 pytest_build_system:
   extends: .test_build_system_template
+  parallel: 3
   artifacts:
     paths:
       - XUNIT_RESULT.xml
@@ -784,7 +785,8 @@ pytest_build_system:
   script:
     - ${IDF_PATH}/tools/ci/test_configure_ci_environment.sh
     - cd ${IDF_PATH}/tools/test_build_system
-    - pytest --work-dir ${CI_PROJECT_DIR}/test_build_system --junitxml=${CI_PROJECT_DIR}/XUNIT_RESULT.xml
+    - pytest --parallel-count ${CI_NODE_TOTAL:-1} --parallel-index ${CI_NODE_INDEX:-1}
+      --work-dir ${CI_PROJECT_DIR}/test_build_system --junitxml=${CI_PROJECT_DIR}/XUNIT_RESULT.xml
 
 build_docker:
   extends: