ci: deny warnings for rustdoc.

This commit updates the CI config to also deny warnings from `rustdoc`.

One finding related to a malformed HTML tag is fixed to ensure CI passes
with this new config.

Author: cpu

.github/workflows/ci.yml

@@ -9,6 +9,7 @@ on:
 
 env:
   RUSTFLAGS: -D warnings
+  RUSTDOCFLAGS: -D warnings
 
 jobs:
   rustfmt:

src/lib.rs

@@ -353,7 +353,7 @@ impl DnType {
 pub enum DnValue {
     /// A string of characters from the T.61 character set
     TeletexString(Vec<u8>),
-    /// An ASCII string containing only A-Z, a-z, 0-9, '()+,-./:=? and <SPACE>
+    /// An ASCII string containing only A-Z, a-z, 0-9, '()+,-./:=? and `<SPACE>`
     PrintableString(String),
     /// A string encoded using UTF-32
     UniversalString(Vec<u8>),