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

@@ -18,8 +18,13 @@ jobs:
           - windows-2019
           - ubuntu-latest
     runs-on: ${{ matrix.os }}
+    env:
+      # dictated by `firefox` to support the `helix` editor, but now driven by the `time` crate. IMPORTANT: adjust etc/msrv-badge.svg as well
+      rust_version: 1.67.0
     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
+      - run: |
+          rustup toolchain install $rust_version --profile minimal --no-self-update
+          rustup default $rust_version
       - run: just ci-check-msrv