ICU-23247 Fix Errorprone ReturnValueIgnored error

[mihnita]

Checklist

• Required: Issue filed: ICU-23247
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
• Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable
• Approver: Feel free to merge on my behalf

[jira-pull-request-webhook]

Notice: the branch changed across the force-push!

• icu4j/main/common_tests/src/test/java/com/ibm/icu/dev/test/format/DateFormatTest.java is now changed in the branch
• icu4j/main/common_tests/src/test/java/com/ibm/icu/dev/test/format/NumberFormatTest.java is now changed in the branch
• icu4j/main/common_tests/src/test/java/com/ibm/icu/dev/test/serializable/SerializableChecker.java is now changed in the branch
• icu4j/main/common_tests/src/test/java/com/ibm/icu/dev/test/util/CurrencyTest.java is now changed in the branch

View Diff Across Force-Push

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