Update doc/gitlab-basics/create-your-ssh-keys.md

What does this MR do?

Updated file in accordance with Vale test output:

doc/gitlab-basics/create-your-ssh-keys.md
 10:1   suggestion  Use "it's" instead of "It is",  gitlab.ContractionsKeep    
                    for a friendly, informal tone.                             
 11:26  warning     Avoid using future tense:       gitlab.FutureTense         
                    "will need"                                                
 28:25  suggestion  Use "can't" instead of          gitlab.ContractionsKeep    
                    "cannot", for a friendly,                                  
                    informal tone.                                             
 28:47  suggestion  Use "did not" instead of        gitlab.ContractionsDiscard 
                    "didn't", for a friendly,                                  
                    informal tone.                                             
 29:2   warning     Avoid using future tense:       gitlab.FutureTense         
                    "will not"                                                 
 30:5   warning     Avoid using future tense:       gitlab.FutureTense         
                    "will need"                    

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