WebSockets Next: fix OnOpen callback that returns Buffer/byte[] #41949

Job	Run time
Attach pull request number	4s
CI Sanity Check	31s
Initial JDK 17 Build	10m 14s
Calculate Test Jobs	9s
JVM Tests - JDK 17	8m 20s
JVM Tests - JDK 21	6m 57s
Devtools Tests - JDK ${{ matrix.java.name }}	0s
Gradle Tests - JDK ${{ matrix.java.name }}	0s
Kubernetes Tests - JDK ${{ matrix.java.name }}	0s
JVM Tests - JDK 17 Windows	10m 7s
Maven Tests - JDK ${{ matrix.java.name }}	0s
Native Tests - ${{ matrix.category }}	0s
Quickstarts Compilation - JDK 17	10m 55s
MicroProfile TCKs Tests	0s
Native Tests - Virtual Thread - ${{ matrix.category }}	0s
Upload build stats to collector	0s
Build report	34s
	47m 51s

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