Remove warning and fix primary constructor use.

Author: khalidabuhakmeh

src/Htmx.TagHelpers/HtmxConfigMetaTagHelper.cs

@@ -311,8 +311,8 @@ public class HtmxTriggerSpecificationCache: Dictionary<string, HtmxTriggerSpecif
 
 public class HtmxTriggerSpecification
 {
-    [JsonPropertyName("trigger")]
-    public string Trigger { get;  set; }
+    [JsonPropertyName("trigger")] 
+    public string Trigger { get;  set; } = default!;
     [JsonPropertyName("sseEvent")]
     public string? SseEvent { get; set; }
     [JsonPropertyName("eventFilter")]

test/Htmx.Tests/HtmxTriggerSpecificationTests.cs

@@ -6,8 +6,15 @@
 
 namespace Htmx.Tests;
 
-public class HtmxTriggerSpecificationTests(ITestOutputHelper outputHelper)
+public class HtmxTriggerSpecificationTests
 {
+    private readonly ITestOutputHelper outputHelper;
+
+    public HtmxTriggerSpecificationTests(ITestOutputHelper outputHelper)
+    {
+        this.outputHelper = outputHelper;
+    }
+    
     private const string Specifications =
         // lang=json
         """