mrhlpr.frontend: Fix string representation of ActionType
Previously, the string representation for ActionType would be something
like ActionType.OK instead of [OK ] as intended. This resulted in
commands like $ mrhlpr status
getting an output like this:
ActionType.OK Changes allowed
ActionType.OK Clean worktree
ActionType.NOK Rebase on master
ActionType.NOK MR-ID in commit msgs
ActionType.NOK Commit subjects follow format
668526 doesn't match any regex
ActionType.NOK Commits are signed
instead of the intended
[OK ] Changes allowed
[OK ] Clean worktree
[NOK] Rebase on master
[NOK] MR-ID in commit msgs
[NOK] Commit subjects follow format
668526 doesn't match any regex
[NOK] Commits are signed
Fixes 8647dd3b