remove f-string flag

Author: dpr-0

Lib/asyncio/streams.py

@@ -409,7 +409,7 @@ def __del__(self, warnings=warnings):
             try:
                 self.close()
             except RuntimeError:
-                warnings.warn(f"loop is closed", ResourceWarning)
+                warnings.warn("loop is closed", ResourceWarning)
             else:
                 warnings.warn(f"unclosed {self!r}", ResourceWarning)