patch 8.2.2619: Vim9: no test for return type of lambda

Problem:    Vim9: no test for return type of lambda.
Solution:   Add a test.

src/testdir/test_vim9_func.vim

@@ -752,11 +752,26 @@ def Test_call_lambda_args()
   CheckDefFailure(lines, 'E1167:')
 enddef
 
+def FilterWithCond(x: string, Cond: func(string): bool): bool
+  return Cond(x)
+enddef
+
 def Test_lambda_return_type()
   var lines =<< trim END
     var Ref = (): => 123
   END
   CheckDefAndScriptFailure(lines, 'E1157:', 1)
+
+  # this works
+  for x in ['foo', 'boo']
+    echo FilterWithCond(x, (v) => v =~ '^b')
+  endfor
+
+  # this fails
+  lines =<< trim END
+      echo FilterWithCond('foo', (v) => v .. '^b')
+  END
+  CheckDefAndScriptFailure(lines, 'E1013: Argument 2: type mismatch, expected func(string): bool but got func(any): string', 1)
 enddef
 
 def Test_lambda_uses_assigned_var()

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2619,
 /**/
     2618,
 /**/