[BUG] org.opensearch.ingest.common.CopyProcessorTests.testCopyWithRemoveSource is flaky

[gaobinlong]

Describe the bug

The test fails when the targetField's name is same to the source field's name but overrideTarget is false, even though we use random() to generate both of the field names, but there's a probability that they are same.

java.lang.IllegalArgumentException: target field [c] already exists
	at __randomizedtesting.SeedInfo.seed([505149C6724DFA24:534B5A60D6CE3A91]:0)
	at org.opensearch.ingest.common.CopyProcessor.execute(CopyProcessor.java:100)
	at org.opensearch.ingest.common.CopyProcessorTests.testCopyWithRemoveSource(CopyProcessorTests.java:78)
	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)

Related component

Indexing

To Reproduce

./gradlew ':modules:ingest-common:test' --tests "org.opensearch.ingest.common.CopyProcessorTests.testCopyWithRemoveSource" -Dtests.seed=505149C6724DFA24 -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=de-LU -Dtests.timezone=Asia/Jerusalem -Druntime.java=21

Expected behavior

The test always pass.

Additional Details

Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [3.0.0-snapshot]