Why is my catch not working on the adderror on contentversion see:

trigger NoteOnContentversion on ContentVersion (before insert, before update) {
     for (ContentVersion c : Trigger.new)  {
        if (c.ContentDocumentId != null) {
            for (ContentDocumentLink link : [
                SELECT LinkedEntityId
                FROM ContentDocumentLink
                WHERE ContentDocumentId = :c.ContentDocumentId
            ]){
                Id parentId = link.LinkedEntityId;
                System.debug('link.LinkedEntityId '+ link);

                Boolean isOrderRegel = parentId.getSObjectType() == Orderregel__c.SObjectType;

                if (isOrderRegel && Approval.isLocked(parentId)){
                  c.addError('Approval pending. You do not have the permission to edit this note, please contact your administrator.');
                }
            }
        }
    }
}

Test class

@IsTest(seeAllData=false)
private class TestNoteOnContentversion {
    
    @IsTest 
    static void refuse_shouldAddError_whenOrderregelIsLocked() {
        // arrange
        Account acc = new Account(
            Name = 'TEST_ACCT', 
            Account_Status_DS__c = 'Status'
        );
        insert acc;
        
        Orderregel__c orderregel = new Orderregel__c(
            Account__c = acc.Id,
            Orderbegindatum__c = Date.today()
        );
        
        insert orderregel;
        
        ContentVersion content=new ContentVersion(); 
        content.Title='Header_Picture1'; 
        content.PathOnClient='/' + content.Title + '.jpg'; 
        Blob bodyBlob=Blob.valueOf('Unit Test ContentVersion Body'); 
        content.VersionData=bodyBlob; 
        //content.LinkedEntityId=sub.id;
        content.origin = 'H';
        insert content;
        
        ContentDocumentLink contentlink=new ContentDocumentLink();
        contentlink.LinkedEntityId=acc.id;
        contentlink.contentdocumentid=[select contentdocumentid from contentversion where id =: content.id].contentdocumentid;
        contentlink.ShareType = 'V';
       
        //insert contentlink;

        List<Account> accts = [SELECT Id from Account WHERE Name = 'TEST_ACCT'];
        
        //lock the account record.
        Approval.LockResult[] lrList = Approval.lock(accts, false);

        Test.startTest();
        try { 
              insert contentlink;
            }
        catch (Exception dmx) 
        { 
           Boolean expectedExceptionThrown = dmx.getMessage().contains('Approval pending. You do not have the permission to edit this note, please contact your administrator.') ? true : false; 
           System.assertEquals(expectedExceptionThrown, true);  
        }
        Test.stopTest();
    }   
}