fix(indents/yaml): only indent mapping pair if value is a block

This improves the following situation, in which '|' is the cursor position:

```yaml
- key1: value1
  key2: value2|
```

Before this commit, by pressing Enter would result in this indentation:

```yaml
- key1: value1
  key2: value2
    |
```

Which is less convenient than this:

```yaml
- key1: value1
  key2: value2
  |
```

queries/yaml/indents.scm

@@ -1,5 +1,5 @@
 [
-  (block_mapping_pair)
+  (block_mapping_pair value: (block_node))
   (block_sequence_item)
 ] @indent