Test mixed case header capture for kafka interceptors (#14529)

Author: laurit

instrumentation/kafka/kafka-clients/kafka-clients-2.6/library/build.gradle.kts

@@ -36,7 +36,7 @@ tasks {
       excludeTestsMatching("WrapperSuppressReceiveSpansTest")
     }
     jvmArgs("-Dotel.instrumentation.messaging.experimental.receive-telemetry.enabled=true")
-    systemProperty("otel.instrumentation.messaging.experimental.capture-headers", "test-message-header")
+    systemProperty("otel.instrumentation.messaging.experimental.capture-headers", "Test-Message-Header")
   }
 
   check {

instrumentation/kafka/kafka-clients/kafka-clients-2.6/library/src/test/java/io/opentelemetry/instrumentation/kafkaclients/v2_6/AbstractInterceptorsTest.java

@@ -54,7 +54,7 @@ void testInterceptors() throws InterruptedException {
           producerRecord
               .headers()
               // add header to test capturing header value as span attribute
-              .add("test-message-header", "test".getBytes(StandardCharsets.UTF_8))
+              .add("Test-Message-Header", "test".getBytes(StandardCharsets.UTF_8))
               // adding baggage header in w3c baggage format
               .add(
                   "baggage",

instrumentation/kafka/kafka-clients/kafka-clients-2.6/library/src/test/java/io/opentelemetry/instrumentation/kafkaclients/v2_6/InterceptorsTest.java

@@ -45,7 +45,7 @@ void assertTraces() {
                       .hasParent(trace.getSpan(0))
                       .hasAttributesSatisfyingExactly(
                           equalTo(
-                              stringArrayKey("messaging.header.test_message_header"),
+                              stringArrayKey("messaging.header.Test_Message_Header"),
                               singletonList("test")),
                           equalTo(MESSAGING_SYSTEM, "kafka"),
                           equalTo(MESSAGING_DESTINATION_NAME, SHARED_TOPIC),
@@ -70,7 +70,7 @@ void assertTraces() {
                         .hasLinksSatisfying(links -> assertThat(links).isEmpty())
                         .hasAttributesSatisfyingExactly(
                             equalTo(
-                                stringArrayKey("messaging.header.test_message_header"),
+                                stringArrayKey("messaging.header.Test_Message_Header"),
                                 singletonList("test")),
                             equalTo(MESSAGING_SYSTEM, "kafka"),
                             equalTo(MESSAGING_DESTINATION_NAME, SHARED_TOPIC),
@@ -87,7 +87,7 @@ void assertTraces() {
                         .hasLinks(LinkData.create(producerSpanContext.get()))
                         .hasAttributesSatisfyingExactly(
                             equalTo(
-                                stringArrayKey("messaging.header.test_message_header"),
+                                stringArrayKey("messaging.header.Test_Message_Header"),
                                 singletonList("test")),
                             equalTo(MESSAGING_SYSTEM, "kafka"),
                             equalTo(MESSAGING_DESTINATION_NAME, SHARED_TOPIC),