increase parallelism in selected artifact and distribtest jobs (#28227)

tools/internal_ci/linux/grpc_build_artifacts.sh

@@ -26,4 +26,4 @@ set -e  # rvm commands are very verbose
 rvm --default use ruby-2.4.1
 set -ex
 
-tools/run_tests/task_runner.py -f artifact linux -j 6
+tools/run_tests/task_runner.py -f artifact linux -j 12

tools/internal_ci/linux/grpc_distribtests.sh

@@ -37,4 +37,4 @@ set -ex
 mv ${KOKORO_GFILE_DIR}/github/grpc/artifacts input_artifacts || true
 ls -R input_artifacts || true
 
-tools/run_tests/task_runner.py -f distribtest linux -j 6
+tools/run_tests/task_runner.py -f distribtest linux -j 12

tools/internal_ci/linux/grpc_distribtests_python.sh

@@ -26,7 +26,7 @@ source tools/internal_ci/helper_scripts/prepare_build_linux_rc
 source tools/internal_ci/helper_scripts/prepare_qemu_rc
 
 # Build all python linux artifacts (this step actually builds all the binary wheels and source archives)
-tools/run_tests/task_runner.py -f artifact linux python -j 6 -x build_artifacts/sponge_log.xml || FAILED="true"
+tools/run_tests/task_runner.py -f artifact linux python -j 12 -x build_artifacts/sponge_log.xml || FAILED="true"
 
 # the next step expects to find the artifacts from the previous step in the "input_artifacts" folder.
 rm -rf input_artifacts
@@ -48,7 +48,7 @@ cp -r artifacts/* input_artifacts/ || true
 # Run all python linux distribtests
 # We run the distribtests even if some of the artifacts have failed to build, since that gives
 # a better signal about which distribtest are affected by the currently broken artifact builds.
-tools/run_tests/task_runner.py -f distribtest linux python -j 6 -x distribtests/sponge_log.xml || FAILED="true"
+tools/run_tests/task_runner.py -f distribtest linux python -j 12 -x distribtests/sponge_log.xml || FAILED="true"
 
 if [ "$FAILED" != "" ]
 then