CI: tell dependabot to not update the MSRV

Co-Authored-By: danieleades <[email protected]>

Author: Philippe-Cholet

.github/workflows/ci.yml

@@ -41,7 +41,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: taiki-e/install-action@cargo-no-dev-deps
-      - uses: dtolnay/[email protected]
+      - uses: dtolnay/rust-toolchain@master
+        with:
+          # Here, it does not trigger a PR from dependabot.
+          toolchain: 1.43.1
       - run: cargo no-dev-deps check
 
   test: