Discrepancy between spec and tests on indexing TypedDicts with unknown literal keys

Splitting issue from PR https://github.com/python/typing/pull/1978

Spec says that indexing with unknown literal keys should be reported as an error:

The use of a key that is not known to exist should be reported as an error, even if this wouldn’t necessarily generate a runtime type error. These are often mistakes, and these may insert values with an invalid type if structural assignability hides the types of certain items. For example, d[‘x’] = 1 should generate a type check error if ‘x’ is not a valid key for d (which is assumed to be a TypedDict type).

But it's not reflected in conformance tests (https://github.com/python/typing/blob/2d88da2a407b556f5b52b4c6ad1bd659873bb9ac/conformance/tests/typeddicts_operations.py) and there's a bit of discrepancy between type checkers how they handle some cases (most of them reject all cases that may cause runtime error / allow cases that do not cause runtime error ).

Would be great if we can either adapt conformance tests to the spec or amend the spec to remove the ambiguity.

Related discussion - https://discuss.python.org/t/typeddict-operations-with-unknown-literal-keys/89653 (also has information on state of this issue in different type checkers).

Vergleiche die zitierte Spezifikationsanforderung mit conformance/tests/typeddicts_operations.py und prüfe anschließend die verlinkte Diskussion sowie den zugehörigen PR auf das unterschiedliche Verhalten der Type-Checker. Kläre, ob die Conformance-Tests oder die Spezifikation geändert werden sollte; abgeschlossen bedeutet, dass die Unklarheit beseitigt ist und Spezifikation und Tests übereinstimmen.