ignore: add some 'allow(dead_code)' annotations

I don't usually like doing this and would prefer to just delete unused
code, but I don't have the context required to understand why this code
is unused. A refresh of this crate is on the (distant) horizon, so I'll
just leave these here for now to squash the warnings.

crates/ignore/src/overrides.rs

@@ -23,9 +23,11 @@ use crate::{
 /// The lifetime `'a` refers to the lifetime of the matcher that produced
 /// this glob.
 #[derive(Clone, Debug)]
+#[allow(dead_code)]
 pub struct Glob<'a>(GlobInner<'a>);
 
 #[derive(Clone, Debug)]
+#[allow(dead_code)]
 enum GlobInner<'a> {
     /// No glob matched, but the file path should still be ignored.
     UnmatchedIgnore,