patch 8.2.2629: Vim9: error for #{{ is not desired

Problem:    Vim9: error for #{{ is not desired.
Solution:   Adjust the checks. (closes #7990)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 67bcc73..d82d2b8 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -5234,7 +5234,8 @@
 	return TRUE;
 #ifdef FEAT_EVAL
     if (in_vim9script())
-	return c == '#' && cmd[1] != '{'
+	//  # starts a comment, #{ might be a mistake, #{{ can start a fold
+	return c == '#' && (cmd[1] != '{' || cmd[2] == '{')
 				 && (cmd == cmd_start || VIM_ISWHITE(cmd[-1]));
 #endif
     return c == '"';