Revert change to vale linting command in lint-doc.sh

What does this MR do and why?

The change in a3731036 seemed to cause vale to fail to lint properly when a lot of files are listed. As a result, a large MR could have vale pass in that pipeline, but when it runs on master with a simple **/*.md, it finally checks the correct files, then fails: gitlab-org/quality/engineering-productivity/master-broken-incidents#5812 (comment 1853039843)

This reverts that change, which causes the correct files to be linted by vale (finding the issues), which I've verified to work locally:

┃  vale ❯ 

 doc/user/application_security/api_security_testing/configuration/offline_configuration.md
 9:197  error  Remove this duplicate word:     gitlab.Repetition 
               'testing'.                                        

 doc/user/application_security/api_security_testing/index.md
 9:1  error  History items must follow       gitlab.HistoryItemsOrder 
             the tier, offering, or status                            
             details.                                                 

 doc/user/application_security/api_security_testing/performance.md
 17:21  error  Remove this duplicate word:     gitlab.Repetition 
               'testing'.                                        
 57:30  error  Remove this duplicate word:     gitlab.Repetition 
               'testing'.                                        

✖ 4 errors, 0 warnings and 0 suggestions in 72 files.
ERROR: Fix any linting errors and make sure you are using the latest version of Vale.

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