remove dtolnay action in favor of plain rustup calls

Using it when availble as standard tool seems preferable over using an action
that potentially hides away what's truly going on (after all, it also calls `rustup`
under the hood)

Author: Byron

.github/workflows/msrv.yml

@@ -20,6 +20,10 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@1.67.0 # dictated by `firefox` to support the `helix` editor, but now driven by the `time` crate. IMPORTANT: adjust etc/msrv-badge.svg as well
       - uses: extractions/setup-just@v2
+      # dictated by `firefox` to support the `helix` editor, but now driven by the `time` crate. IMPORTANT: adjust etc/msrv-badge.svg as well
+      - run: |
+          export version=1.67.0
+          rustup toolchain install $version --profile minimal --no-self-update
+          rustup default $version
       - run: just ci-check-msrv