`DescriptorType` has wrong `Display` impl for variant `Cov`

[RCasatta]

Display impl

elements-miniscript/src/descriptor/mod.rs

Line 118 in af410f6

DescriptorType::Cov => write!(f, "elcovwsh"),

has "el" prepended but the FromStr impl seems to not have it

elements-miniscript/src/descriptor/mod.rs

Line 151 in af410f6

} else if s.len() >= 6 && &s[0..6] == "covwsh" {