CI: Bump dtolnay/rust-toolchain from v1 to master

Fixes deprecation warnings from GHA.

Author: guihkx

.github/actions/setup-rust/action.yml

@@ -16,7 +16,7 @@ runs:
   using: composite
   steps:
     - name: Install Rust toolchain
-      uses: dtolnay/rust-toolchain@v1
+      uses: dtolnay/rust-toolchain@master
       with:
         toolchain: ${{ inputs.toolchain }}
         target: ${{ inputs.target }}