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GH-38832: [Java] Avoid building twice in `ci/scripts/java_build.sh` (#38829)

### Rationale for this change

`ci/scripts/java_build.sh` can invoke `mvn install` several times on the Arrow Java codebase. This happens especially in JNI and Integration builds, which have some optional components enabled.

### What changes are included in this PR?

Only invoke `mvn install` once. This change seems to save around 5 minutes on the JNI and Integration builds.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.

* Closes: #38832

Lead-authored-by: Antoine Pitrou <pitrou@free.fr>
Co-authored-by: Antoine Pitrou <antoine@python.org>
Co-authored-by: david dali susanibar arce <davi.sarces@gmail.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>