desc in .case files cannot start with [ (even if quoted)

[nicolo-ribaudo]

See #4341.

When you have a .case file that contains desc: "[foo] bar" and a .template that has desc: baz, the generator will create a test that has desc: [foo] bar (baz) (note the missing quotes). This is invalid, as in Yaml that [foo] is parsed as an array.