Fixed link not dispalyed in markup in Style.cs and added unit test cases

src/Spectre.Console/Style.cs

@@ -226,6 +226,11 @@ public string ToMarkup()
             builder.Add("on " + Background.ToMarkup());
         }
 
+        if (Link?.ToString() != null)
+        {
+            builder.Add($"link={Link.ToString()}");
+        }
+
         return string.Join(" ", builder);
     }
 

src/Tests/Spectre.Console.Tests/Unit/StyleTests.cs

@@ -405,5 +405,31 @@ public void Should_Return_Expected_Markup_For_Style_With_Only_Background_Color()
             // Then
             result.ShouldBe("default on green");
         }
+
+        [Fact]
+        public void Should_Return_Expected_Markup_For_Style_With_Only_Link()
+        {
+            // Given
+            var style = new Style(link:"https://spectreconsole.net/");
+
+            // When
+            var result = style.ToMarkup();
+
+            // Then
+            result.ShouldBe("link=https://spectreconsole.net/");
+        }
+
+        [Fact]
+        public void Should_Return_Expected_Markup_For_Style_With_Background_And_Link()
+        {
+            // Given
+            var style = new Style(background: Color.Blue, link: "https://spectreconsole.net/");
+
+            // When
+            var result = style.ToMarkup();
+
+            // Then
+            result.ShouldBe("default on blue link=https://spectreconsole.net/");
+        }
     }
 }