set IS_VALGRIND envrionment variable (#608)

Author: Vipul-Cariappa

.github/actions/Build_and_Test_cppyy/action.yml

@@ -121,7 +121,9 @@ runs:
           else
             SUPPRESSION_FILE="../etc/${CLANG_INTERPRETER}${CLANG_VERSION}-valgrind.supp"
           fi
+          export IS_VALGRIND=true
           valgrind --show-error-list=yes --error-exitcode=1 --track-origins=yes --gen-suppressions=all --suppressions="${SUPPRESSION_FILE}" --suppressions=../etc/valgrind-cppyy-cling.supp python -m pytest -m "not xfail" -sv -ra --ignore=test_leakcheck.py
+          unset IS_VALGRIND
         fi
         export RETCODE=+$?
         echo ::endgroup::