mypy reports false-positive [exhaustive-match] error when there is an unreachable match

**Bug Report** `exhaustive-match` incorrectly reports a missing `A` case when using a capture pattern (`case A() as a`) together with an unreachable extra branch. The following code reports: ```text error: Match statement has unhandled case for values of type "A" [exhaustive-match] ``` even though all possible values of `A | None` are handled. Interestingly, the error disappears if the unreachable `case B():` branch is removed. This seems related to exhaustiveness analysis for class patterns with `as` captures. **To Reproduce** ```python # mypy: enable-error-code=exhaustive-match class A: pass class B: pass x: A | None match x: case None: pass case A() as a: pass case B(): pass ``` **Expected Behavior** No errors should be reported. `x` has type `A | None`, and both `None` and `A` are handled exhaustively. The `case B():` branch is unreachable and should not affect exhaustiveness checking. Removing the `case B():` branch currently makes mypy report no errors: ```python match x: case None: pass case A() as a: pass ``` **Actual Behavior** ```text main.py:8: error: Match statement has unhandled case for values of type "A" [exhaustive-match] main.py:8: note: If match statement is intended to be non-exhaustive, add `case _: pass` Found 1 error in 1 file (checked 1 source file) ``` **Your Environment** - Mypy version used: 2.1.0 - Mypy command-line flags: `--enable-error-code exhaustive-match` - Mypy configuration options from `mypy.ini` (and other config files): none - Python version used: 3.13 - see https://mypy-play.net/?mypy=2.1.0&python=3.13&enable-error-code=exhaustive-match&gist=027087d73156a9153fe92b49b19c9ce9