chore(CI): mpl head step for rust (#1583)

Author: josecorella

.github/workflows/library_rust_tests.yml

@@ -13,6 +13,11 @@ on:
         required: false
         default: false
         type: boolean
+      mpl-head:
+        description: "Running on MPL HEAD"
+        required: false
+        default: false
+        type: boolean
 
 jobs:
   testRust:
@@ -59,6 +64,15 @@ jobs:
         with:
           dafny-version: nightly-2024-12-03-4954170
 
+      - name: Update MPL submodule if using MPL HEAD
+        if: ${{ inputs.mpl-head == true }}
+        working-directory: submodules/MaterialProviders
+        run: |
+          git checkout main
+          git pull
+          git submodule update --init --recursive
+          git rev-parse HEAD
+
       # Remove this after the formatting in Rust starts working
       - name: smithy-dafny Rust hacks
         shell: bash