chore(deps): bump undici to 6.28.0 (#305)

## Summary
Dependency sweep — security bump (within existing range):
- `undici` 6.27.0 → 6.28.0 (medium) — resolves 3 Dependabot alerts in
`.github/actions/version-matrix/yarn.lock`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: apify-deps[bot] <4649591+apify-deps[bot]@users.noreply.github.com>

Author: apify-deps[bot]

.github/actions/version-matrix/yarn.lock

@@ -356,9 +356,9 @@ __metadata:
   linkType: hard
 
 "undici@npm:^6.23.0":
-  version: 6.27.0
-  resolution: "undici@npm:6.27.0"
-  checksum: 10/30c18cdb235edf4dd36f8aa3ace1ffaf44060289a7d62ad44c33180d2d74a224015d25574812f62ce9c625b5beb1b0b766495b650fedf356aca11eed7ce2c816
+  version: 6.28.0
+  resolution: "undici@npm:6.28.0"
+  checksum: 10/672a7a53bd1f6c80edb73b357ab36e98ef9e474024c442aab2b8ea2bc32f1103cab05525c78661ae724f3e1340e23d03efb9730fba28e76218ab0ec52e15d75a
   languageName: node
   linkType: hard