[Yaml] Fix comment containing a colon on a scalar line being parsed as a hash.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Note: I only ran the Yaml Component tests.

This PR fixes a bug in YAML parsing where a comment containing a colon followed by a space, like this:

    foo # warning: this is a scalar with a comment, not a hash

was parsed as a hash, resulting in:

    array( 'foo # warning' => 'this is a scalar with a comment, not a hash' )

instead of:

    'foo'