Disable some System.Net.WebHeaderCollection tests on Mono. (#26862)

Author: Martin Baulig

src/System.Net.WebHeaderCollection/tests/LoggingTest.cs

@@ -11,6 +11,7 @@ public class WebHeaderCollectionLoggingTest
     {
         [ActiveIssue(20470, TargetFrameworkMonikers.UapAot)]
         [Fact]
+        [SkipOnTargetFramework(TargetFrameworkMonikers.Mono, "NetEventSource is only part of .NET Core")]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "NetEventSource is only part of .NET Core")]
         public void EventSource_ExistsWithCorrectId()
         {

src/System.Net.WebHeaderCollection/tests/WebHeaderCollectionTest.cs

@@ -543,6 +543,7 @@ public void Add_InvalidHeader_ThrowsArgumentException(string header, string para
         private const string CookieInvalid = "helloWorld";
 
         [Fact]
+        [SkipOnTargetFramework(TargetFrameworkMonikers.Mono, "Does not work in Mono")]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "Requires fix shipping in .NET 4.7.2")]
         public void GetValues_MultipleSetCookieHeadersWithExpiresAttribute_Success()
         {
@@ -561,6 +562,7 @@ public void GetValues_MultipleSetCookieHeadersWithExpiresAttribute_Success()
         }
 
         [Fact]
+        [SkipOnTargetFramework(TargetFrameworkMonikers.Mono, "Does not work in Mono")]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "Requires fix shipping in .NET 4.7.2")]
         public void GetValues_SingleSetCookieHeaderWithMultipleCookiesWithExpiresAttribute_Success()
         {
@@ -609,6 +611,7 @@ public void GetValues_SingleSetCookieHeaderWithMultipleCookiesWithNoAttribute_Su
         }
 
         [Fact]
+        [SkipOnTargetFramework(TargetFrameworkMonikers.Mono, "Does not work in Mono")]
         [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "Requires fix shipping in .NET 4.7.2")]
         public void GetValues_InvalidSetCookieHeader_Success()
         {