## Problem
We created extensions in a single database. The tests could interfere,
i.e., discover some service tables left by other extensions and produce
unexpected results.
## Summary of changes
The tests are now run in a separate timeline, so only one extension owns
the database, which prevents interference.
## Problem
The nightly test discovered problems in the extensions upgrade test.
1. `PLv8` has different versions on PGv17 and PGv16 and a different test
set, which was not implemented correctly
[sample](https://github.com/neondatabase/neon/actions/runs/13382330475/job/37372930271)
2. The same for `semver`
[sample](https://github.com/neondatabase/neon/actions/runs/13382330475/job/37372930017)
3. `pgtap` interfered with the other tests, e.g. tables, created by
other extensions caused the tests to fail.
## Summary of changes
The discovered problems were fixed.
1. The tests list for `PLv8` is now generated using the original
Makefile
2. The patches for `semver` are now split for PGv16 and PGv17.
3. `pgtap` is being tested in a separate database now.
---------
Co-authored-by: Mikhail Kot <mikhail@neon.tech>
