Try caching cargo

.github/workflows/main.yml

@@ -29,6 +29,21 @@ jobs:
         with:
           toolchain: stable
           override: true
+      - name: Cache cargo registry
+        uses: actions/cache@v1
+        with:
+          path: ~/.cargo/registry
+          key: ${{ runner.os }}-cargo-registry-${{ hashFiles('**/Cargo.lock') }}
+      - name: Cache cargo index
+        uses: actions/cache@v1
+        with:
+          path: ~/.cargo/git
+          key: ${{ runner.os }}-cargo-index-${{ hashFiles('**/Cargo.lock') }}
+      - name: Cache cargo build
+        uses: actions/cache@v1
+        with:
+          path: target
+          key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('**/Cargo.lock') }}
       - name: Install cargo-tarpaulin
         uses: actions-rs/cargo@v1
         with: