MINOR: Add license header in suppressions.xml

[ruanwenjun]

I find there is no Apache License header in suppressions.xml, this pr is adding the license header.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[showuon]

@ruanwenjun , thanks for the patch. Left a comment.

[showuon]

Is this necessary to add this line?

[ruanwenjun]

Thanks for your review.
To be honestly, I am not sure if this is must, but from the demo provided by checkstyle, it contains this header.
So it might be better to add this header.
https://maven.apache.org/plugins/maven-checkstyle-plugin/examples/suppressions-filter.html

[showuon]

OK, from the XML spec [1], it said:

XML documents SHOULD begin with an XML declaration which specifies the version of XML being used.

Adding it to follow the spec suggestion is good to me.
1: https://www.w3.org/TR/xml/#sec-prolog-dtd

[showuon]

failed tests are unrelated:

[Build / JDK 11 and Scala 2.13 / kafka.server.DynamicBrokerReconfigurationTest.testThreadPoolResize()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11753/1/testReport/junit/kafka.server/DynamicBrokerReconfigurationTest/Build___JDK_11_and_Scala_2_13___testThreadPoolResize__/)
    [Build / JDK 11 and Scala 2.13 / kafka.server.DynamicBrokerReconfigurationTest.testThreadPoolResize()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11753/1/testReport/junit/kafka.server/DynamicBrokerReconfigurationTest/Build___JDK_11_and_Scala_2_13___testThreadPoolResize___2/)
    Build / JDK 8 and Scala 2.12 / org.apache.kafka.connect.integration.ConnectorRestartApiIntegrationTest.testMultiWorkerRestartOnlyConnector
    [Build / JDK 8 and Scala 2.12 / kafka.api.ConsumerBounceTest.testClose()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11753/1/testReport/junit/kafka.api/ConsumerBounceTest/Build___JDK_8_and_Scala_2_12___testClose__/)
    [Build / JDK 17 and Scala 2.13 / kafka.server.DynamicBrokerReconfigurationTest.testThreadPoolResize()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11753/1/testReport/junit/kafka.server/DynamicBrokerReconfigurationTest/Build___JDK_17_and_Scala_2_13___testThreadPoolResize__/)
    [Build / JDK 17 and Scala 2.13 / kafka.server.DynamicBrokerReconfigurationTest.testThreadPoolResize()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11753/1/testReport/junit/kafka.server/DynamicBrokerReconfigurationTest/Build___JDK_17_and_Scala_2_13___testThreadPoolResize___2/)

[showuon]

LGTM! Thanks for the patch, and help format the license header in xml files.