Improve readability by using str

src/_pytest/config/__init__.py

@@ -658,7 +658,7 @@ def _importconftest(
                 if dirpath in path.parents or path == dirpath:
                     if mod in mods:
                         raise RuntimeError(
-                            f"{conftestpath=} has already been loaded as the module {mod=}"
+                            f"{str(conftestpath)=} has already been loaded as the module {mod=}"
                         )
                     mods.append(mod)
         self.trace(f"loading conftestmodule {mod!r}")