GitHub workflow update (test multiple Bitcoin Core versions)

* 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.

.github/workflows/unittests.yml

@@ -4,12 +4,13 @@ on: [push, pull_request]
 
 jobs:
   build:
-    name: python ${{ matrix.python-version }} on ${{ matrix.os }}
+    name: python ${{ matrix.python-version }}, bitcoind ${{ matrix.bitcoind-version }} on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os: [macos-latest, ubuntu-latest]
         python-version: ["3.7", "3.8", "3.9", "3.10", "3.11"]
+        bitcoind-version: ["0.18.0", "25.0"]
 
     steps:
       - uses: actions/checkout@v3
@@ -38,10 +39,13 @@ jobs:
         uses: actions/cache@v3
         env:
           cache-name: bitcoind
+          BITCOIND_VERSION: ${{ matrix.bitcoind-version }}
         with:
           path: ~/bitcoin/*/bin/bitcoin*
-          key: ${{ runner.os }}-${{ env.cache-name }}-${{ hashFiles('test/testrunner/install_bitcoind.sh') }}
+          key: ${{ runner.os }}-${{ env.cache-name }}-${{ env.BITCOIND_VERSION }}-${{ hashFiles('test/testrunner/install_bitcoind.sh') }}
       - name: Install bitcoind
+        env:
+          BITCOIND_VERSION: ${{ matrix.bitcoind-version }}
         run: ./test/testrunner/install_bitcoind.sh
       - name: Cache miniircd
         uses: actions/cache@v3

test/testrunner/install_bitcoind.sh

@@ -2,12 +2,19 @@
 
 set -ev
 
-export BITCOIND_VERSION=0.19.1
+if [[ -z "$BITCOIND_VERSION" ]]; then
+    echo "BITCOIND_VERSION must be set"
+    exit 1
+fi
 
 if [[ "$(uname)" == "Linux" ]]; then
     platform="x86_64-linux-gnu"
 elif [[ "$(uname)" == "Darwin" ]]; then
-    platform="osx64"
+    if [[ $BITCOIND_VERSION > 23.0 || $BITCOIND_VERSION == 23.0 ]]; then
+        platform="x86_64-apple-darwin"
+    else
+        platform="osx64"
+    fi
 else
     echo "Unsupported platform: $(uname)"
     exit 1