Set JAVA_APP_DIR env var when necessary #38197

Job	Run time
CI Sanity Check	32s
Attach pull request number	2s
Initial JDK 17 Build	11m 11s
Calculate Test Jobs	11s
JVM Tests - JDK 17	7m 34s
Kubernetes Tests - JDK 17	4m 4s
Maven Tests - JDK ${{ matrix.java.name }}	0s
JVM Tests - JDK 21	5m 57s
Gradle Tests - JDK ${{ matrix.java.name }}	0s
Kubernetes Tests - JDK 21	4m 0s
Kubernetes Tests - JDK 17 Windows	2m 46s
JVM Tests - JDK 17 Windows	4m 26s
Quickstarts Compilation - JDK 17	5m 41s
Native Tests - ${{ matrix.category }}	0s
MicroProfile TCKs Tests	0s
Native Tests - Virtual Thread - ${{ matrix.category }}	0s
Devtools Tests - JDK ${{ matrix.java.name }}	0s
Build report	32s
	46m 56s

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