Fix missing error when redeclaring type variable in nested generic class

[brianschubert]

Closes #10479

Fixes a case where mypy doesn't warn about an inner generic class using a type variable by the same name as an outer generic class if the inner generic class doesn't declare the type variable using Generic, Protocol, or PEP-695 syntax.

[brianschubert]

Typing conformance diff for this PR (generics_scoping now passes 🎉):

diff --git a/conformance/results/mypy/generics_scoping.toml b/conformance/results/mypy/generics_scoping.toml
index d9be0a0..d588666 100644
--- a/conformance/results/mypy/generics_scoping.toml
+++ b/conformance/results/mypy/generics_scoping.toml
@@ -11,6 +11,7 @@ generics_scoping.py:54: error: Type variable "generics_scoping.S" is unbound  [v
 generics_scoping.py:54: note: (Hint: Use "Generic[S]" or "Protocol[S]" base class to bind "S" inside a class)
 generics_scoping.py:54: note: (Hint: Use "S" in function signature to bind "S" inside a function)
 generics_scoping.py:65: error: Free type variable expected in Generic[...]  [misc]
+generics_scoping.py:75: error: Type variable "T" is bound by an outer class  [valid-type]
 generics_scoping.py:78: error: Type variable "generics_scoping.T" is unbound  [valid-type]
 generics_scoping.py:78: note: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class)
 generics_scoping.py:78: note: (Hint: Use "T" in function signature to bind "T" inside a function)
@@ -25,7 +26,6 @@ generics_scoping.py:96: error: Type variable "generics_scoping.T" is unbound  [v
 generics_scoping.py:96: note: (Hint: Use "Generic[T]" or "Protocol[T]" base class to bind "T" inside a class)
 generics_scoping.py:96: note: (Hint: Use "T" in function signature to bind "T" inside a function)
 """
-conformance_automated = "Fail"
+conformance_automated = "Pass"
 errors_diff = """
-Line 75: Expected 1 errors
 """
diff --git a/conformance/results/mypy/version.toml b/conformance/results/mypy/version.toml
index e3a8b6e..7162661 100644
--- a/conformance/results/mypy/version.toml
+++ b/conformance/results/mypy/version.toml
@@ -1,2 +1,2 @@
-version = "mypy 1.16.0+dev.e867132134c7b8046ebae2d6e1fa9fc184b9e9d7"
-test_duration = 4.9
+version = "mypy 1.16.0+dev.dd0f577f1caebfcd944fb247086af6150e6f1b02"
+test_duration = 5.3

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[hauntsaninja]

Great!