set IS_VALGRIND envrionment variable (#145)

Author: Vipul-Cariappa

.github/workflows/Ubuntu.yml

@@ -598,7 +598,9 @@ jobs:
         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 --suppressions="${SUPPRESSION_FILE}" --suppressions=../etc/valgrind-cppyy-cling.supp python -m pytest -m "not xfail" -sv -ra
+        unset IS_VALGRIND
         export RETCODE=+$?
         echo ::endgroup::