Merge bitcoin/bitcoin#25650: script: default to necessary tags in test/get_previous_releases.py

21a9e94dbb ci: remove hardcoded tag list from ci scripts (josibake)
d530ba390e doc: update test/README.md (josibake)
614d4682ba script: default to necessary tags in get_previous_releases.py (josibake)

Pull request description:

  Almost every time I need to use this script, I forget the tag list is needed and that a specific set of tags is needed for the backwards compatibility tests to work. I end up wasting time reading through the script and googling to find the tag list before remembering it is in `test/README.md`

  I assume (hope) I'm not the only one this happens to, so I figured it would make more sense to have the script default to downloading/building the necessary tags. This has the added benefit of making the script the source of truth: the script already needs to be updated with the SHA256_SUM of the binary for every new tag that is added, so it makes sense to use `SHA256_SUMS` list as the necessary tag list. This means there is less risk of the README and the script drifting (i.e updating the readme with a new tag and forgetting to update the script, or updating the script and forgetting to update the README). Now all that needs to happen is to update the `SHA256_SUMS` list in the script and everything Just Works (TM)

ACKs for top commit:
  Sjors:
    re-tACK 21a9e94dbb

Tree-SHA512: 97b488227a89a6827584edd251820a7074fad75dfd7f26f1aa5f858e2521d2e02effd0f11e6dc4676e1155d3d5aba6ff94a4b58ffef80dc201376afd5927deb9

ci/test/00_setup_env_native_qt5.sh

@@ -14,6 +14,6 @@ export TEST_RUNNER_EXTRA="--previous-releases --coverage --extended --exclude fe
 export RUN_UNIT_TESTS_SEQUENTIAL="true"
 export RUN_UNIT_TESTS="false"
 export GOAL="install"
-export PREVIOUS_RELEASES_TO_DOWNLOAD="v0.14.3 v0.15.2 v0.16.3 v0.17.2 v0.18.1 v0.19.1 v0.20.1 v0.21.0 v22.0 v23.0"
+export DOWNLOAD_PREVIOUS_RELEASES="true"
 export BITCOIN_CONFIG="--enable-zmq --with-libs=no --with-gui=qt5 --enable-reduce-exports \
 --enable-debug CFLAGS=\"-g0 -O2 -funsigned-char\" CXXFLAGS=\"-g0 -O2 -funsigned-char\" CC=gcc-8 CXX=g++-8"

ci/test/05_before_script.sh

@@ -47,6 +47,6 @@ if [ -z "$NO_DEPENDS" ]; then
   fi
   CI_EXEC "$SHELL_OPTS" make "$MAKEJOBS" -C depends HOST="$HOST" "$DEP_OPTS" LOG=1
 fi
-if [ -n "$PREVIOUS_RELEASES_TO_DOWNLOAD" ]; then
-  CI_EXEC test/get_previous_releases.py -b -t "$PREVIOUS_RELEASES_DIR" "${PREVIOUS_RELEASES_TO_DOWNLOAD}"
+if [ "$DOWNLOAD_PREVIOUS_RELEASES" = "true" ]; then
+  CI_EXEC test/get_previous_releases.py -b -t "$PREVIOUS_RELEASES_DIR"
 fi