Avoid StringIndexOutOfBoundsException in KafkaRuntimeConfigProducer #41020

Job	Run time
Attach pull request number	6s
CI Sanity Check	33s
Initial JDK 17 Build	13m 16s
Calculate Test Jobs	16s
Kubernetes Tests - JDK 17	13m 18s
Gradle Tests - JDK ${{ matrix.java.name }}	0s
JVM Tests - JDK 17	11m 47s
Kubernetes Tests - JDK 21	12m 30s
Devtools Tests - JDK ${{ matrix.java.name }}	0s
Kubernetes Tests - JDK 17 Windows	17m 45s
Maven Tests - JDK 17	8m 0s
Maven Tests - JDK 17 Windows	11m 57s
Quickstarts Compilation - JDK 17	6m 4s
JVM Tests - JDK 21	13m 5s
Native Tests - Messaging1	31m 33s
JVM Tests - JDK 17 Windows	7m 51s
Native Tests - HTTP	6m 46s
MicroProfile TCKs Tests	0s
Native Tests - Virtual Thread - Messaging	4m 17s
Build report	38s
	2h 39m 42s

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