[Yaml] Fixed the escaping of strings starting with a dash when dumping

Dashes need to be escaped in character sets in regexes as they are used to specify a range otherwise.
It fixes the dumper bug reported in #9039 (the parsing issue is not fix here)

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | partially #9039
| License       | MIT
| Doc PR        | n/a