* Add support for testing against multiple Bitcoin Core versions, add
0.18.0 (oldest officially support for test suite) and 25.0 (latest
stable release). Previously we tested against hardcoded 0.19.1. IMO
testing against oldest supported and latest makes sense, if tests pass
on both, they should pass on releases inbetween too, unless there is
some behaviour affecting us changed twice.
* Update actions/cache from v2 to v3.
Also changed Core downloads from bitcoin.org to bitcoincore.org.
Kristaps Kaupe
undeath