Suppress laudatory summary output when no assertions are executed.

[wtn]

Suggest to drop the "checkered flag" & rabbit emoji when no tests run.

This patch swaps in "black flag" for this case. I would have chosen "white flag" but that doesn't align well due to rendering issues in macOS.

Any desired changes are OK with me.

Before

With errors

0 assertions
🏁 Finished in 26.0µs; 0.0 assertions per second.
🐇 No slow tests found! Well done!

🔥 Errored assertions:
file test/example.rb:1
   ⚠ LoadError: cannot load such file -- test_helper

After

With errors

0 assertions
🏴 Finished in 32.0µs.

🔥 Errored assertions:
file test/example.rb:1
   ⚠ LoadError: cannot load such file -- test_helper

No errors

0 assertions
🏴 Finished in 450.0µs.

Types of Changes

• New feature.

Contribution

• I added tests for my changes.
• I tested my changes locally.
• I agree to the Developer's Certificate of Origin 1.1.

[ioquatix]

Thanks!