What is the best way to organize the storage of a script in git for different versions of php?

Question

PHP

There is a script which works on php 5.6.
There was a desire to rewrite it and optimize it for php 7.
Tell me how best to organize the storage of the script in git for different versions of php?
To make it convenient to develop and update several versions at once.
Maybe in different repositories? Or in different branches?
And how convenient will it be to make the same changes in such conditions?

Answer 1

Create multiple branches for different versions.