Add pyupgrade linter

This ensures we use the best syntax for the minimal Python version used.
The linter found one issue, fixed with the auto-fixer.

fastapi_cache/coder.py

@@ -52,7 +52,7 @@ def object_hook(obj: Any) -> Any:
     if _spec_type in CONVERTERS:
         return CONVERTERS[_spec_type](obj["val"])
     else:
-        raise TypeError("Unknown {}".format(_spec_type))
+        raise TypeError(f"Unknown {_spec_type}")
 
 
 class Coder:

pyproject.toml

@@ -86,6 +86,7 @@ select = [
     "F", # pyflakes
     "I", # isort
     "W", # pycodestyle warnings
+    "UP", # pyupgrade
 ]
 target-version = "py37"