Avoid bundling package.json

- `package.json` is bundled by `esbuild` because we depend on it in `actions-util.ts`
- That is so we can access the `version` property
- We now use `build.mjs` to define a constant for it instead
- We also set this constant in `ava.setup.mjs` for tests
- This reduces the size of the generated `.js` files and avoids changing them entirely in some cases

ava.config.mjs

@@ -5,4 +5,5 @@ export default {
     },
     compile: false,
   },
+  require: ["./ava.setup.mjs"],
 };