fix(test): use default tag_pattern for tests

git-cliff-core/tests/integration_test.rs

@@ -44,7 +44,7 @@ fn generate_changelog() -> Result<()> {
 			},
 		]),
 		filter_commits:       Some(true),
-		tag_pattern:          String::new(),
+		tag_pattern:          None,
 		skip_tags:            None,
 	};
 

git-cliff/src/changelog.rs

@@ -188,7 +188,7 @@ mod test {
 					},
 				]),
 				filter_commits:       Some(false),
-				tag_pattern:          String::new(),
+				tag_pattern:          None,
 				skip_tags:            Regex::new("v3.*").ok(),
 			},
 		};