Fix msrv: Run msrv checks with minimal versions

Since it is possible to for dependencies to bump MSRV in patch release, msrv checking should use the minimal versions supported by gix.

Users cares deeply about msrv can also pin them to the minimal versions to maintain their current msrv.

.github/workflows/msrv.yml

@@ -30,6 +30,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: extractions/setup-just@v2
       - run: |
-          rustup toolchain install ${{ env.rust_version }} --profile minimal --no-self-update
+          rustup toolchain install ${{ env.rust_version }} nightly --profile minimal --no-self-update
           rustup default ${{ env.rust_version }}
+          cargo +nightly update -Zminimal-versions
       - run: just ci-check-msrv