setup: downgrade linux runner to fix hashlib<->openssl problems

[ixje]

CI started to fail because the openssl people thought it was smart to make ripemd160 optional and move it to legacy. Python depends on this and will now fail because the ubuntu-latest test runner has this "new" openssl version that makes it legacy. After a huge out lash by tons of developers on their decision they re-enabled it in this commit with a blogpost here. This commit is included in openssl 3.0.7. The test runner doesn't have this version and it's not yet installable through apt because instead the Ubuntu security team back ported some security patch and openssl is still on 3.0.2. So the easiest way to fix this is just go back to an old test runner until the runner is updated with openssl 3.0.7

[coveralls]

Coverage remained the same at 80.93% when pulling 7805f1b on fix-ci into 12b5a35 on master.