userdiff: support enum keyword in PHP hunk header

"enum" keyword will be introduced in PHP 8.1.
https://wiki.php.net/rfc/enumerations

Signed-off-by: USAMI Kenta <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: zonuexe

t/t4018/php-enum

@@ -0,0 +1,4 @@
+enum RIGHT: string
+{
+    case Foo = 'ChangeMe';
+}

userdiff.c

@@ -214,7 +214,7 @@ PATTERNS("perl",
 	 "|<<|<>|<=>|>>"),
 PATTERNS("php",
 	 "^[\t ]*(((public|protected|private|static|abstract|final)[\t ]+)*function.*)$\n"
-	 "^[\t ]*((((final|abstract)[\t ]+)?class|interface|trait).*)$",
+	 "^[\t ]*((((final|abstract)[\t ]+)?class|enum|interface|trait).*)$",
 	 /* -- */
 	 "[a-zA-Z_][a-zA-Z0-9_]*"
 	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+"