editorial: add code tag

Co-authored-by: Emil Lundberg <emil@yubico.com>

index.bs

@@ -2200,7 +2200,7 @@ When this method is invoked, the user agent MUST execute the following algorithm
                 ::  whose value is an {{AuthenticationExtensionsClientOutputs}} object containing [=extension identifier=] →
                     [=client extension output=] entries. The entries are created by running each extension's
                     [=client extension processing=] algorithm to create the [=client extension outputs=], for each
-                    [=client extension=] in |options|.{{PublicKeyCredentialRequestOptions/extensions}}.
+                    [=client extension=] in <code>|options|.{{PublicKeyCredentialRequestOptions/extensions}}</code>.
 
             1.  Let |constructAssertionAlg| be an algorithm that takes a [=global object=]
                 |global|, and whose steps are: