Bump mysql2 from 3.9.1 to 3.9.4

Bumps [mysql2](https://github.com/sidorares/node-mysql2) from 3.9.1 to 3.9.4.
- [Release notes](https://github.com/sidorares/node-mysql2/releases)
- [Changelog](https://github.com/sidorares/node-mysql2/blob/master/Changelog.md)
- [Commits](sidorares/node-mysql2@v3.9.1...v3.9.4)

---
updated-dependencies:
- dependency-name: mysql2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

package.json

@@ -21,7 +21,7 @@
   },
   "dependencies": {
     "@iobroker/adapter-core": "3.0.4",
-    "mysql2": "3.9.1"
+    "mysql2": "3.9.4"
   },
   "devDependencies": {
     "@alcalzone/release-script": "3.7.0",