version.php is altered even though no upgrade took place

[flobeier]

I accidentally tried to upgrade from NC 13 to 15. It was an old instance that hasn't been updated in a while.

Problem: After starting the Nextcloud instance with the Docker images of NC 15 I got log entries that skipping a major version isn't supported. I went back to NC 14 images but got a log entry that said that the instance is already on version 15 and downgrading is not supported.

Cause: The version.php file in the data folder was replaced by the NC 15 images. Why? I think that shouldn't happen when no upgrade took place. I had to manually replace the version.php with the right one from a NC 13 zip file.