[configparser] Fix missing fallback argument in SectionProxy.get (#13559)

Closes: #13556

stdlib/@tests/test_cases/check_configparser.py

@@ -0,0 +1,5 @@
+from configparser import RawConfigParser, SectionProxy
+from typing_extensions import assert_type
+
+sp = SectionProxy(RawConfigParser(), "")
+assert_type(sp.get("foo", fallback="hi"), str)

stdlib/configparser.pyi

@@ -320,7 +320,14 @@ class SectionProxy(MutableMapping[str, str]):
     # This is incompatible with MutableMapping so we ignore the type
     @overload  # type: ignore[override]
     def get(
-        self, option: str, *, raw: bool = False, vars: _Section | None = None, _impl: Any | None = None, **kwargs: Any
+        self,
+        option: str,
+        fallback: None = None,
+        *,
+        raw: bool = False,
+        vars: _Section | None = None,
+        _impl: Any | None = None,
+        **kwargs: Any,  # passed to the underlying parser's get() method
     ) -> str | None: ...
     @overload
     def get(
@@ -331,7 +338,7 @@ class SectionProxy(MutableMapping[str, str]):
         raw: bool = False,
         vars: _Section | None = None,
         _impl: Any | None = None,
-        **kwargs: Any,
+        **kwargs: Any,  # passed to the underlying parser's get() method
     ) -> str | _T: ...
     # These are partially-applied version of the methods with the same names in
     # RawConfigParser; the stubs should be kept updated together