fix(sumtype): template canMatch does not account for ref when matching

The template `canMatch` does not account for `ref`.
The template `valueTypes` stores all types of the member values and uses SumTypes's `get` function, which returns a `ref`.
However, ref does not persist and the type is not sent to `canMatch` as a `ref`.
Because of this, when matching, `canMatch` will fail as it will test for a copy, and returning a reference of that value results in escaping it.

Fix Issue 23101

Signed-off-by: João Lourenço <jlourenco5691@gmail.com>

Author: iK4tsu

std/sumtype.d

@@ -1830,7 +1830,7 @@ class MatchException : Exception
 template canMatch(alias handler, Ts...)
 if (Ts.length > 0)
 {
-    enum canMatch = is(typeof((Ts args) => handler(args)));
+    enum canMatch = is(typeof((ref Ts args) => handler(args)));
 }
 
 ///