Enable CentOS Stream 9 in PR workflows

It should work just fine and other than CS9, there are no other
platforms enabled ATM.

.github/workflows/pr_checks.yaml

@@ -10,8 +10,6 @@ permissions:
 
 jobs:
   centos_stream9:
-    # pylint is not available for centos_stream9, disable for now
-    if: false
     runs-on: ubuntu-latest
     container:
       image: quay.io/centos/centos:stream9

tests/run_suite.sh

@@ -23,7 +23,7 @@ ANABOT_DIR=`pwd`
 #DOGTAIL_DIR=`install_dogtail $ANABOT_DIR/dogtail/dogtail-*.tar.gz`
 # pylint's return code is bit-ORed value of statuses. See pylint manpage.
 # 3 means: 1 - fatal message + 2 - error message
-${PYLINT:-pylint} --init-hook="import site; site.addsitedir('./lib/python2.7/site-packages/')" anabot; PYLINT_RETCODE=$?
+${PYLINT:-pylint} --init-hook="import site; site.addsitedir('./lib/python3.9/site-packages/')" anabot; PYLINT_RETCODE=$?
 test $[PYLINT_RETCODE & 3] -ne 0 && SCORE=$[SCORE+1]
 
 #rm -rf -- "$DOGTAIL_DIR"