fix incorrect handling of Assertion failure for no_prompt mode

[mashehu]

in no_prompt mode we never wrote to self.error, which caused nf-core m test -p to always be successful.

closes #4227

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.37%. Comparing base (e66ecde) to head (4744d36).
⚠️ Report is 4 commits behind head on dev.

Files with missing lines	Patch %	Lines
nf_core/components/components_test.py	50.00%	3 Missing ⚠️

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.