Update sideEffects property in package.json

[NullVoxPopuli]

Followup to #21456

This should resolve the issue that the ecosystem-ci nightly run found https://github.com/NullVoxPopuli/ember-ecosystem-ci/actions/runs/28985574086/job/86013935001

  Error: Attempted to use test utilities, but `ember-testing` was not included
                at testingNotAvailableMessage (webpack://__ember_auto_import__/../node_modules/.pnpm/ember-source@file+..+..+..+ember-source-main.tgz_@glimmer+component@2.1.1/node_modules/ember-source/dist/dev/packages/@ember/test/index.js?:8:93)
                at Object.<anonymous> (http://localhost:7357/assets/tests.js:457:32)

(affected ember-qunit, and @ember/test-waiters only )

Note

In our app blueprint, we import ember-testing directly, so this is normally a non-issue. https://github.com/ember-cli/ember-app-blueprint/blob/feddd39c5f4e0de2b8cf3afb6003d00b353eccf8/files/tests/index.html#L33

[github-actions]

📊 Size report

Tarball size — 1.2 MB → 1.2 MB

dist/dev   No changes

File	Before (Size / Brotli)	After (Size / Brotli)
./packages/shared-chunks/api-{hash}.js	26.2 kB / 5.8 kB	-61.6%↓10 kB / -63.5%↓2.1 kB
./packages/shared-chunks/template-{hash}.js	1.1 kB / 401 B	-54%↓491 B / -49.4%↓203 B
Total (Includes all files)	2.1 MB / 497.5 kB	2.1 MB / 497.5 kB

---

dist/prod   No changes

File	Before (Size / Brotli)	After (Size / Brotli)
Total (Includes all files)	1.9 MB / 454.9 kB	1.9 MB / 454.9 kB

---

smoke-tests/v2-app-template/dist   No changes

File	Before (Size / Brotli)	After (Size / Brotli)
Total (Includes all files)	350.2 kB / 95.6 kB	350.2 kB / 95.6 kB

---

smoke-tests/v2-app-hello-world-template/dist   No changes

File	Before (Size / Brotli)	After (Size / Brotli)
Total (Includes all files)	132.5 kB / 37.1 kB	132.5 kB / 37.1 kB

_{🤖 This report was automatically generated by wyvox/pkg-size}