Pin exact librt instead of lower bound

Author: jhance

mypy-requirements.txt

@@ -4,4 +4,6 @@ typing_extensions>=4.6.0
 mypy_extensions>=1.0.0
 pathspec>=0.9.0
 tomli>=1.1.0; python_version<'3.11'
-librt>=0.5.0
+# pin exact version; its okay to allow a range of versions only when its known
+# that the entire range has the same abi version
+librt==0.5.0