Run node tests

Currently we have a job for each supported version of Bitcoin Core and
in it we run the integration tests.

Note also that `node` is currently not a member of the workspace. So it
misses out on all the benefits of `run_task` (e.g., linting).

However `node` cannot be directly run using `run_task` because of its
unusual features but since we already have the `Integration` job set up
to manage these features we can just run the `node` tests from there
also. This has the added advantage that the same downloaded Bitcoin Core
binary will be used (I hope).

Add a script and call it from the `Integration` job. In the script first
run the `node` tests and then run the integration tests.

Author: tcharding

.github/workflows/rust.yaml

@@ -232,4 +232,4 @@ jobs:
       - name: "Select toolchain"
         uses: dtolnay/rust-toolchain@stable
       - name: "Run integration tests"
-        run: cd integration_test && cargo test --features=${{ matrix.feature }}
+        run: ./contrib/version_specific_tests.sh ${{ matrix.feature }}