Fixed failing unit test.

Author: AndyButland

tests/Umbraco.AuthorizedServices.Tests/Services/AuthorizedRequestBuilderTests.cs

@@ -39,9 +39,10 @@ public async Task CreateRequestMessage_ReturnsExpectedResult()
         var content = await stringContent!.ReadAsStringAsync();
         content.Should().Be("{\"Foo\":\"bar\"}");
 
-        result.Headers.Count().Should().Be(2);
+        result.Headers.Count().Should().Be(3);
         result.Headers.Authorization!.ToString().Should().Be("Bearer 1234");
         result.Headers.UserAgent.ToString().Should().Be("UmbracoServiceIntegration/1.0.0");
+        result.Headers.Accept!.ToString().Should().Be("application/json");
     }
 
     private class TestRequestData