Bump netty4_version from 4.2.0.Final to 4.2.1.Final (#15375)

Bumps `netty4_version` from 4.2.0.Final to 4.2.1.Final.

Updates `io.netty:netty-all` from 4.2.0.Final to 4.2.1.Final
- [Commits](netty/netty@netty-4.2.0.Final...netty-4.2.1.Final)

Updates `io.netty:netty-bom` from 4.2.0.Final to 4.2.1.Final
- [Commits](netty/netty@netty-4.2.0.Final...netty-4.2.1.Final)

---
updated-dependencies:
- dependency-name: io.netty:netty-all
  dependency-version: 4.2.1.Final
  dependency-type: direct:development
  update-type: version-update:semver-patch
- dependency-name: io.netty:netty-bom
  dependency-version: 4.2.1.Final
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

dubbo-dependencies-bom/pom.xml

@@ -95,7 +95,7 @@
     <javassist_version>3.30.2-GA</javassist_version>
     <byte-buddy_version>1.17.5</byte-buddy_version>
     <netty_version>3.2.10.Final</netty_version>
-    <netty4_version>4.2.0.Final</netty4_version>
+    <netty4_version>4.2.1.Final</netty4_version>
     <netty_http3_version>0.0.29.Final</netty_http3_version>
     <httpclient_version>4.5.14</httpclient_version>
     <httpcore_version>4.4.16</httpcore_version>