Superfluous new line between key and a long value after to_yaml()

For long values updated in a yaml file it seems that an unexpected new line is added between key and value (after colon):

```
devid: xxxxyxyxyx-9eeeee-412ae-8342-2c6436dsrff
token:
v^1.1#i^1#p^3 ...............................XX== (2500 characters!)
```
The expected format is
```
devid: xxxxyxyxyx-9eeeee-412ae-8342-2c6436dsrff
token: v^1.1#i^1#p^3 ...............................XX==
```
Because of the newline the token is unusable.

Start by locating the to_yaml() implementation and reproduce the issue with a value around 2500 characters in a YAML file. Check the generated output around the key and colon; done means the long token remains on the same line as its key and remains usable.

Written by the indexing model from the issue text.