Use non-capturing group in arg pattern regex (#3006)

Author: casey

src/pattern.rs

@@ -18,7 +18,7 @@ impl Pattern {
       .map_err(|source| token.error(CompileErrorKind::ArgumentPatternRegex { source }))?;
 
     Ok(Self(
-      format!("^({})$", literal.cooked)
+      format!("^(?:{})$", literal.cooked)
         .parse::<Regex>()
         .map_err(|source| token.error(CompileErrorKind::ArgumentPatternRegex { source }))?,
     ))
@@ -27,7 +27,7 @@ impl Pattern {
 
 impl Display for Pattern {
   fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-    write!(f, "{}", &self.0.as_str()[2..self.0.as_str().len() - 2])
+    write!(f, "{}", &self.0.as_str()[4..self.0.as_str().len() - 2])
   }
 }