Fix: Use emoji

Author: localheinz

.github/CONTRIBUTING.md

@@ -104,7 +104,7 @@ make static-code-analysis-baseline
 
 to regenerate the baseline in [`../phpstan-baseline.neon`](../phpstan-baseline.neon).
 
-:exclamation: Ideally, the baseline should shrink over time.
+❗️ Ideally, the baseline should shrink over time.
 
 ## Tests