[flang] Merge pull request flang-compiler/f18#721 from flang-compiler/pmk-fix-errormsg

Fix expected error messages in tests to correspond with recent update…

Original-commit: flang-compiler/f18@ffbc017c45527a3ac4825cbe33e732eee1f0ecee
Reviewed-on: https://github.com/flang-compiler/f18/pull/721