Add cargo insta install step to ci

.github/workflows/tests.yml

@@ -13,6 +13,10 @@ jobs:
         with:
           toolchain: stable
       - uses: Swatinem/rust-cache@v2
+      - name: Install cargo insta
+        uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-insta
       - name: Check
         run: make check
       - name: Test