[red-knot] mypy_primer: Use upstream repo (#17500)

## Summary

Switch to the official version of
[`mypy_primer`](https://github.com/hauntsaninja/mypy_primer), now that
Red Knot support has been upstreamed (see
https://github.com/hauntsaninja/mypy_primer/pull/138,
https://github.com/hauntsaninja/mypy_primer/pull/135,
https://github.com/hauntsaninja/mypy_primer/pull/151,
https://github.com/hauntsaninja/mypy_primer/pull/155).

## Test Plan

Locally and in CI

.github/workflows/mypy_primer.yaml

@@ -45,7 +45,7 @@ jobs:
 
       - name: Install mypy_primer
         run: |
-          uv tool install "git+https://github.com/astral-sh/mypy_primer.git@add-red-knot-support-v6"
+          uv tool install "git+https://github.com/hauntsaninja/mypy_primer@ebaa9fd27b51a278873b63676fd25490cec6823b"
 
       - name: Run mypy_primer
         shell: bash