ci: fix test file references and hardcoded paths

- Remove non-existent test_mime_detection.py from unit tests
- Use relative paths in security tests for container compatibility

tests/security/profiled_server.py

@@ -7,8 +7,9 @@ import io
 import pstats
 import signal
 import sys
+from pathlib import Path
 
-sys.path.insert(0, "/home/user/git/flaskpaste")
+sys.path.insert(0, str(Path(__file__).parent.parent.parent))
 
 from app import create_app