fix(settings): Add some context to the PHP memory limit error

[joshtrichards]

Summary

See nextcloud/updater#505, nextcloud/updater#316

Obviously impacts various features and apps, not just the updater, but that's what brought this up again.

TODO

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• [ ] Tests (unit, integration, api and/or acceptance) are included
• [ ] Screenshots before/after for front-end changes
• [ ] Documentation (manuals or wiki) has been updated or is not required
• [ ] Backports requested where applicable (ex: critical bugfixes)