ci: Cache the install of tarpaulin

Author: bluss

.github/workflows/ci.yml

@@ -88,7 +88,9 @@ jobs:
         with:
           toolchain: ${{ matrix.rust }}
       - name: Install tarpaulin
-        run: cargo install cargo-tarpaulin -f
+        uses: taiki-e/cache-cargo-install-action@v2
+        with:
+          tool: cargo-tarpaulin
       - name: Generate code coverage
         run: cargo tarpaulin --verbose --all-features --workspace --timeout 120 --out Xml
       - name: Upload to codecov.io