scanner: fix nested multiline comments (#17859)

vlib/v/scanner/scanner.v

@@ -1071,7 +1071,7 @@ fn (mut s Scanner) text_scan() token.Token {
 							s.inc_line_number()
 							continue
 						}
-						if s.expect('/*', s.pos) {
+						if s.expect('/*', s.pos) && s.text[s.pos + 2] != `/` {
 							nest_count++
 							continue
 						}

vlib/v/tests/nested_multiline_comments_test.v

@@ -1,5 +1,19 @@
-fn test_nested_multiline_comments() {
+fn test_nested_multiline_comments_1() {
 	/*//println(os.args)
 	*/
 	assert true
 }
+
+fn test_nested_multiline_comments_2() {
+	tt()
+	assert true
+}
+
+/*
+fn tt() {
+}
+//*/
+
+fn tt() {
+	println('hello, world')
+}