The regular expression in the new test is intended to match the
documented [1] ABNF for a media type:
type-name = reg-name
subtype-name = reg-name
reg-name = 1*127reg-name-chars
reg-name-chars = ALPHA / DIGIT / "!" /
"#" / "$" / "&" / "." /
"+" / "-" / "^" / "_"
Closes gh-29746
[1] https://datatracker.ietf.org/doc/html/rfc4288#section-4.2