Pin Test Suite CI job to 1.84.0 so the metrics 0.23.0 dep compiles (matches lint/clippy job)

Author: dcadenas

.github/workflows/rust.yml

@@ -10,11 +10,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Install stable toolchain
+      - name: Install pinned toolchain
         uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: stable
+          toolchain: 1.84.0
           override: true
 
       - name: Run tests