docs: fix policy-checking command example (#3527)

Documentation does not match the implementated command introduced by #3351

runatlantis.io/docs/policy-checking.md

@@ -23,7 +23,7 @@ Any failures need to either be addressed in a successive commit, or approved by
 
 Policy approvals may be cleared either by re-planing, or by issuing the following command:
 ```
-atlantis approve_policies --clear-policy-approvals
+atlantis approve_policies --clear-policy-approval
 ```
 
 ::: warning
@@ -190,4 +190,4 @@ When the policy check workflow runs, a file is created in the working directory
   }
 ]
 
-```
+```