KTOR-7278: fix accept header evaluation

[anton-erofeev]

Subsystem
Server, ktor-server-core

Motivation
https://youtrack.jetbrains.com/issue/KTOR-7278

Solution
fixed Content-Type header evaluation

[bjhham]

Please check the CI - looks like this change breaks another test https://ktor.teamcity.com/buildConfiguration/Ktor_KtorMatrixCoreLinuxJava17/273217?expandBuildDeploymentsSection=false&hideTestsFromDependencies=false&hideProblemsFromDependencies=false&expandPull+Request+Details=true&expandBuildChangesSection=true&expandBuildTestsSection=true

[osipxd]

Please check the CI

It seems like our CI is not reachable for community, so here are the logs:

io.ktor.tests.server.routing.RoutingProcessingTest
  testAcceptHeaderProcessing()[jvm] - FAILED

org.opentest4j.AssertionFailedError: expected: <OK> but was: <>
  at app//kotlin.test.junit5.JUnit5Asserter.assertEquals(JUnitSupport.kt:32)
  at app//kotlin.test.AssertionsKt__AssertionsKt.assertEquals(Assertions.kt:63)
  at app//kotlin.test.AssertionsKt.assertEquals(Unknown Source)
  at app//kotlin.test.AssertionsKt__AssertionsKt.assertEquals$default(Assertions.kt:62)
  at app//kotlin.test.AssertionsKt.assertEquals$default(Unknown Source)
  at app//io.ktor.tests.server.routing.RoutingProcessingTest$testAcceptHeaderProcessing$1.invokeSuspend(RoutingProcessingTest.kt:496)
  at app//kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
  at app//kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:104)
  at app//kotlinx.coroutines.internal.LimitedDispatcher$Worker.run(LimitedDispatcher.kt:111)
  at app//kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:99)
  at app//kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:584)
  at app//kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:811)
  at app//kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:715)
  at app//kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:702)