patch 8.2.4536: debugger test fails when breaking on expression

Problem:    Debugger test fails when breaking on expression.
Solution:   Compare strings with "==" instead of "is".
diff --git a/src/debugger.c b/src/debugger.c
index 54bf6ba..6c38e5a 100644
--- a/src/debugger.c
+++ b/src/debugger.c
@@ -989,7 +989,12 @@
 		}
 		else
 		{
-		    if (typval_compare(tv, bp->dbg_val, EXPR_IS, FALSE) == OK
+		    // Use "==" instead of "is" for strings, that is what we
+		    // always have done.
+		    exprtype_T	type = tv->v_type == VAR_STRING
+							? EXPR_EQUAL : EXPR_IS;
+
+		    if (typval_compare(tv, bp->dbg_val, type, FALSE) == OK
 			    && tv->vval.v_number == FALSE)
 		    {
 			typval_T *v;