Fixes wp-cli/wp-cli#5960

This PR fixes the issue where wp user update incorrectly exits with 0 when the provided user ID is invalid. Now, when an invalid user ID, email, or login is supplied, the command will return an exit code of 1 instead of 0, ensuring proper error handling.

Testing Instructions

Try updating a non-existent user:
wp user update 9999 --user_pass=securepassword

Expected output:
Warning: Invalid user ID, email or login: '9999'

Expected exit code: 1
echo $?
Should return 1

Try updating a existent user:
wp user update 1 --user_pass=securepassword

Expected output:
Success: Updated user 1.

Expected exit code: 0
echo $?
Should return 0

Screenshot