Exclude Spark runner from UsesKeyInParDo tests

beam_PostCommit_Java_ValidatesRunner_Spark is red.

testKeyInOnTimer fails with:
org.apache.beam.sdk.Pipeline$PipelineExecutionException: java.lang.NumberFormatException: null

testKeyInOnTimerWithGenericKey fails with:
org.apache.beam.sdk.Pipeline$PipelineExecutionException: java.lang.NullPointerException

This can be reproduced locally by running `/gradlew :runners:spark:validatesRunnerBatch --tests "ParDoTest\$KeyTests" --scan`