Bump postcss-discard-comments from 6.0.1 to 7.0.3

Bumps [postcss-discard-comments](https://github.com/cssnano/cssnano) from 6.0.1 to 7.0.3.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/postcss-discard-comments@6.0.1...postcss-discard-comments@7.0.3)

---
updated-dependencies:
- dependency-name: postcss-discard-comments
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

polaris-react/package.json

@@ -103,7 +103,7 @@
     "js-yaml": "^4.1.0",
     "postcss": "^8.3.1",
     "postcss-custom-media": "^10.0.1",
-    "postcss-discard-comments": "^6.0.1",
+    "postcss-discard-comments": "^7.0.3",
     "postcss-import": "^16.1.0 ",
     "postcss-loader": "^4.2.0",
     "postcss-mixins": "^9.0.4",