Re-enabled the rust cargo index and registry caches because

cargo was downloading them just for nothing.
ankitects#528

.github/workflows/checks.yml

@@ -107,17 +107,17 @@ jobs:
       #     path: ${{ matrix.PIP_WHEELS_DIR }}
       #     key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}-12-
 
-      # - name: Cache cargo index
-      #   uses: actions/cache@v1
-      #   with:
-      #     path: ${{ matrix.CARGO_INDEX_DIR }}
-      #     key: ${{ runner.os }}-cargo-index-${{ hashFiles('**/Cargo.toml') }}-12-
+      - name: Cache cargo index
+        uses: actions/cache@v1
+        with:
+          path: ${{ matrix.CARGO_INDEX_DIR }}
+          key: ${{ runner.os }}-cargo-index-${{ hashFiles('**/Cargo.toml') }}-12-
 
-      # - name: Cache cargo registry
-      #   uses: actions/cache@v1
-      #   with:
-      #     path: ${{ matrix.CARGO_REGISTRY_DIR }}
-      #     key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.toml') }}-12-
+      - name: Cache cargo registry
+        uses: actions/cache@v1
+        with:
+          path: ${{ matrix.CARGO_REGISTRY_DIR }}
+          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.toml') }}-12-
 
       - name: Cache cargo target
         uses: actions/cache@v1