Wraps values containing : in runtime_fields test in quotes

[picandocodigo]

Backport of #63660

[elasticmachine]

Pinging @elastic/es-core-infra (:Core/Infra/REST API)

[nik9000]

This is getting pretty crazy. One of us needs to fix our parser. I don't remember which one is in the wrong here.

[picandocodigo]

Thanks @nik9000! The Ruby parser leverages libyaml to parse YAML, and it seems to only have a problem with this particular format: match: {hits.hits.0._explanation.description: day_of_week:Monday}. The error I see is:

found unexpected ':' while scanning a plain scalar

For something like: key: some:value, it's parsed fine. I even tried a different YAML parser and still got a syntax error from the same syntax. From what I've read so far the solution is "just wrap it with quotes" and "It depends on each implementation". But ideally we'd want to find a way to catch these sooner.