Improve version.php script (do not prompt for upgrade after running it)

[marinaglancy]

• do not accidentally bump the core version up
• if we downgraded any plugins or core and moodle does not need upgrade, update the verison hash This way we won't need to run upgrade script after fixing version

[FMCorz]

Thanks Marina.

Have you considered simply running:

mdk run version; mdk upgrade --no-checkout

[marinaglancy]

I run this script on non-mdk installations so it was convenient for me if it does everything out-of-the-box. But if you think it's not needed, ignore this pull request

[marinaglancy]

also my change to line 33 was a bug imho