Mark a doc comment block as text instead of ignore

This way, it won't show up in the output of `cargo test`

ironfish-rust/src/frost_utils/account_keys.rs

@@ -26,7 +26,7 @@ pub struct MultisigAccountKeys {
 
 /// Derives the account keys for a multisig account, realizing the following key hierarchy:
 ///
-/// ```ignore
+/// ```text
 ///                 ak ─┐
 ///                     ├─ ivk ── pk
 ///   gsk ── nsk ── nk ─┘