ci: use rust-toolchain@stable instead of @1.85 in MSRV job

Author: philippemnoel

.github/workflows/ci.yml

@@ -117,7 +117,7 @@ jobs:
       - uses: actions/checkout@v6
 
       - name: Install Rust toolchain (MSRV)
-        uses: dtolnay/rust-toolchain@1.85
+        uses: dtolnay/rust-toolchain@stable
 
       - name: Cache cargo registry and build
         uses: actions/cache@v5