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GH-44830: [Java][CI] Disable Java Dependabot (#44832)



### Rationale for this change

We moved to apache/arrow-java.

### What changes are included in this PR?

Stop running Dependabot for Maven here.

### Are these changes tested?

N/A

### Are there any user-facing changes?

No.
* GitHub Issue: #44830

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: Raúl Cumplido <raulcumplido@gmail.com>