Fix typo

Pointed out in:
#2295 (comment)

Author: emlun

index.bs

@@ -1696,7 +1696,7 @@ The [=[RP]=] SHOULD first use {{PublicKeyCredential/getClientCapabilities()}}
 to check that the [=client=] supports the {{ClientCapability/conditionalCreate}} capability
 in order to prevent a user-visible error in case this feature is not available.
 The client MUST set BOTH |requireUserPresence| and |requireUserVerification| to |FALSE| when <code>|options|.{{CredentialCreationOptions/mediation}}</code> is set to {{CredentialMediationRequirement/conditional}}
-unless they may explicitly performed during the ceremony.
+unless they may be explicitly performed during the ceremony.
 
 Any {{CredentialsContainer/create()|navigator.credentials.create()}} operation can be aborted by leveraging the {{AbortController}};
 see [[dom#abortcontroller-api-integration]] for detailed instructions.