rm 5.5, add 6.5 (#15439)

Author: bakatzir

.github/pull_request_template.md

@@ -20,10 +20,10 @@ A few sentences describing the overall goals of the pull request's commits.
 Paste here any images that will help the reviewer
 
 ## Minimum version of Cortex XSOAR
-- [ ] 5.5.0
 - [ ] 6.0.0
 - [ ] 6.1.0
 - [ ] 6.2.0
+- [ ] 6.5.0
 
 ## Does it break backward compatibility?
    - [ ] Yes