[easy] run typechecking on CI (excalidraw#954)

.github/workflows/lint.yml

@@ -19,5 +19,6 @@ jobs:
           npm ci
           npm run test:other
           npm run test:code
+          npm run test:typecheck
         env:
           CI: true

package.json

@@ -97,6 +97,7 @@
     "test:app": "react-scripts test --env=jsdom --passWithNoTests",
     "test:debug": "react-scripts --inspect-brk test --runInBand --no-cache",
     "test:code": "eslint --ignore-path .gitignore --ext .js,.ts,.tsx .",
+    "test:typecheck": "tsc",
     "test:other": "npm run prettier -- --list-different"
   },
   "version": "1.0.0",

src/element/newElement.test.ts

@@ -41,6 +41,7 @@ it("clones arrow element", () => {
 
   assertCloneObjects(element, copy);
 
+  // @ts-ignore
   expect(copy.__proto__).toEqual({ hello: "world" });
   expect(copy.hasOwnProperty("hello")).toBe(false);