ci: increase mutation testing thresholds

Increase min-msi from 94% to 98% (+4%) and min-covered-msi from 96%
to 98% (+2%) to reflect improved mutation test coverage.

Author: claude

.github/workflows/test.yml

@@ -168,4 +168,4 @@ jobs:
           chmod +x infection.phar
 
       - name: Run mutation testing
-        run: ./infection.phar --threads=max --min-msi=94 --min-covered-msi=96
+        run: ./infection.phar --threads=max --min-msi=98 --min-covered-msi=98