Merge branch 'document-yaml-colon' into 'master'

Clarify CI script needing to quote colons

## What does this MR do?

Clarifies documentation for `.gitlab-ci.yml` `script`.

## Are there points in the code the reviewer needs to double check?

Should this be a note? Is there a link to YAML spec we can point to?

## Why was this MR needed?

## What are the relevant issue numbers?

Closes #20177.

## Screenshots (if relevant)


See merge request !5481

doc/ci/yaml/README.md

@@ -379,6 +379,8 @@ job:
     - bundle exec rspec
 ```
+Sometimes, `script` commands will need to be wrapped in single or double quotes. For example, commands that contain a colon (`:`) need to be wrapped in quotes so that the YAML parser knows to interpret the whole thing as a string rather than a "key: value" pair. Be careful when using special characters (`:`, `{`, `}`, `[`, `]`, `,`, `&`, `*`, `#`, `?`, `|`, `-`, `<`, `>`, `=`, `!`, `%`, `@`, `` ` ``).
+
 ### stage
 `stage` allows to group build into different stages. Builds of the same `stage`