tests: don't run doctests on non-exported macros

Since Rust 1.62.0, doctests on macros are run even if the macro isn't
marked #[macro_export] [0]. Because the macro can't actually be accessed
externally, we explicitly mark the doctest as ignored so it continues
not to be run.

[0]: rust-lang/rust#96630

src/newtype_macros.rs

@@ -172,7 +172,7 @@ macro_rules! public_newtype_traits (($newtype:ident) => (
 /// Usage:
 /// Generating secret datatypes, e.g. keys
 ///
-/// ```
+/// ```ignore
 /// new_type! {
 ///     /// This is some documentation for our type
 ///     secret Key(KEYBYTES);
@@ -181,17 +181,16 @@ macro_rules! public_newtype_traits (($newtype:ident) => (
 ///
 /// Generating public datatypes, e.g. public keys
 ///
-/// ```
+/// ```ignore
 /// new_type! {
 ///     /// This is some documentation for our type
 ///     public PublicKey(PUBLICKEYBYTES);
 /// }
-///
 /// ```
 ///
 /// Generating nonce types
 ///
-/// ```
+/// ```ignore
 /// new_type! {
 ///     /// This is some documentation for our type
 ///     nonce Nonce(NONCEBYTES);