runtime(yaml): Fix flow mapping key detection

fixes: #15196
closes: #15313

Signed-off-by: itchyny <itchyny@cybozu.co.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/syntax/testdir/dumps/yaml_07.dump b/runtime/syntax/testdir/dumps/yaml_07.dump
index ce0d166..ff6d9a2 100644
--- a/runtime/syntax/testdir/dumps/yaml_07.dump
+++ b/runtime/syntax/testdir/dumps/yaml_07.dump
@@ -1,9 +1,10 @@
-| +0&#ffffff0@3|<+0#e000e06&@1|:| +0#0000000&|*+0#00e0003&|f|o@1| +0#0000000&@62
+| +0&#ffffff0@1|b+0#00e0e07&|a|r|:+0#e000e06&| +0#0000000&@68
+@4|<+0#e000e06&@1|:| +0#0000000&|*+0#00e0003&|f|o@1| +0#0000000&@62
 @4|b+0#00e0e07&|a|z|:+0#e000e06&| +0#0000000&|&+0#00e0003&|b|a|r| +0#0000000&@61
 @6|f+0#00e0e07&|o@1|:+0#e000e06&| +0#0000000&|[+0#e000e06&|*+0#00e0003&|f|o@1|]+0#e000e06&| +0#0000000&@57
 @4|q+0#00e0e07&|u|x|:+0#e000e06&| +0#0000000&@66
-@6|<+0#e000e06&@1|:| +0#0000000&|[+0#e000e06&|*+0#00e0003&|f|o@1|,+0#0000000&| |*+0#00e0003&|b|a|r|]+0#e000e06&| +0#0000000&@52
-@2>b+0#00e0e07&|a|z|:+0#e000e06&| +0#0000000&|{+0#e000e06&|<@1|:| +0#0000000&|*+0#00e0003&|f|o@1|,+0#0000000&| |q+0#00e0e07&|u|x|:+0#e000e06&| +0#0000000&|[+0#e000e06&|{|<@1| +0#0000000&|:+0#e000e06&| +0#0000000&|*+0#00e0003&|f|o@1|}+0#e000e06&|]|}| +0#0000000&@37
+@6><+0#e000e06&@1|:| +0#0000000&|[+0#e000e06&|*+0#00e0003&|f|o@1|,+0#0000000&| |*+0#00e0003&|b|a|r|]+0#e000e06&| +0#0000000&@52
+@2|b+0#00e0e07&|a|z|:+0#e000e06&| +0#0000000&|{+0#e000e06&|<@1|:| +0#0000000&|*+0#00e0003&|f|o@1|,+0#0000000&| |q+0#00e0e07&|u|x|:+0#e000e06&| +0#0000000&|[+0#e000e06&|{|<@1| +0#0000000&|:+0#e000e06&| +0#0000000&|*+0#00e0003&|f|o@1|}+0#e000e06&|]|}| +0#0000000&@37
 |~+0#4040ff13&| @73
 |~| @73
 |~| @73
@@ -16,5 +17,4 @@
 |~| @73
 |~| @73
 |~| @73
-|~| @73
-| +0#0000000&@56|1|2|7|,|3| @8|B|o|t| 
+| +0#0000000&@56|1|2|7|,|7| @8|B|o|t|