patch 8.2.3261: Vim9: when compiling repeat(123, N) return type is number

Problem:    Vim9: when compiling repeat(123, N) return type is number.
Solution:   Make return type a string. (closes #8664)

src/evalfunc.c

@@ -930,6 +930,13 @@ ret_first_arg(int argcount, type_T **argtypes)
     if (argcount > 0)
 	return argtypes[0];
     return &t_void;
+}
+    static type_T *
+ret_repeat(int argcount UNUSED, type_T **argtypes)
+{
+    if (argtypes[0] == &t_number)
+	return &t_string;
+    return argtypes[0];
 }
 // for map(): returns first argument but item type may differ
     static type_T *
@@ -1813,7 +1820,7 @@ static funcentry_T global_functions[] =
     {"rename",		2, 2, FEARG_1,	    arg2_string,
 			ret_number_bool,    f_rename},
     {"repeat",		2, 2, FEARG_1,	    arg2_repeat,
-			ret_first_arg,	    f_repeat},
+			ret_repeat,	    f_repeat},
     {"resolve",		1, 1, FEARG_1,	    arg1_string,
 			ret_string,	    f_resolve},
     {"reverse",		1, 1, FEARG_1,	    arg1_list_or_blob,

src/testdir/test_vim9_builtin.vim

@@ -2558,9 +2558,15 @@ enddef
 def Test_repeat()
   CheckDefAndScriptFailure2(['repeat(1.1, 2)'], 'E1013: Argument 1: type mismatch, expected string but got float', 'E1224: String, Number or List required for argument 1')
   CheckDefAndScriptFailure2(['repeat({a: 10}, 2)'], 'E1013: Argument 1: type mismatch, expected string but got dict<', 'E1224: String, Number or List required for argument 1')
-  assert_equal('aaa', repeat('a', 3))
-  assert_equal('111', repeat(1, 3))
-  assert_equal([1, 1, 1], repeat([1], 3))
+  var lines =<< trim END
+      assert_equal('aaa', repeat('a', 3))
+      assert_equal('111', repeat(1, 3))
+      assert_equal([1, 1, 1], repeat([1], 3))
+      var s = '-'
+      s ..= repeat(5, 3)
+      assert_equal('-555', s)
+  END
+  CheckDefAndScriptSuccess(lines)
 enddef
 
 def Test_resolve()

src/version.c

@@ -755,6 +755,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3261,
 /**/
     3260,
 /**/