style(db): remove f-string without placeholders

Replace f-string with regular string in injection pattern warning
since there are no placeholders. Auto-fixed by ruff linter.

Author: Sakeeb91

db/executor.py

@@ -141,7 +141,7 @@ def validate(self, sql: str) -> list[str]:
         # Check for SQL injection patterns
         for pattern in INJECTION_PATTERNS:
             if re.search(pattern, sql_upper):
-                errors.append(f"Potential SQL injection pattern detected")
+                errors.append("Potential SQL injection pattern detected")
                 break
 
         return errors