Fixed `matrix_user_id` regex (#4312)

* fix(matrix_user_id): fixed regex

* test(matrix_user_id): added test with underscore

crates/utils/src/utils/validation.rs

@@ -6,7 +6,7 @@ use url::Url;
 
 // From here: https://github.com/vector-im/element-android/blob/develop/matrix-sdk-android/src/main/java/org/matrix/android/sdk/api/MatrixPatterns.kt#L35
 static VALID_MATRIX_ID_REGEX: Lazy<Regex> = Lazy::new(|| {
-  Regex::new(r"^@[A-Za-z0-9\\x21-\\x39\\x3B-\\x7F]+:[A-Za-z0-9.-]+(:[0-9]{2,5})?$")
+  Regex::new(r"^@[A-Za-z0-9\x21-\x39\x3B-\x7F]+:[A-Za-z0-9.-]+(:[0-9]{2,5})?$")
     .expect("compile regex")
 });
 // taken from https://en.wikipedia.org/wiki/UTM_parameters
@@ -386,6 +386,7 @@ mod tests {
   #[test]
   fn test_valid_matrix_id() {
     assert!(is_valid_matrix_id("@dess:matrix.org").is_ok());
+    assert!(is_valid_matrix_id("@dess_:matrix.org").is_ok());
     assert!(is_valid_matrix_id("@dess:matrix.org:443").is_ok());
     assert!(is_valid_matrix_id("dess:matrix.org").is_err());
     assert!(is_valid_matrix_id(" @dess:matrix.org").is_err());