Merge JoinMarket-Org/joinmarket-clientserver#1820: ci: no fail-fast for unittests

9eaca78600 ci: no fail-fast for unittests (3np)

Pull request description:

  Let all unittest jobs finish to completion even if one in the matrix fails.

  This should make it easier and quicker to distinguish between:
  - Legitimate new regressions affecting all runtimes
  - Flaky tests
  - Differences between runtimes
  - Whether errors are consistent or intermittent

  without manually restarting or retrying.

  https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#jobsjob_idstrategyfail-fast

  Also ensures results for `master` have complete coverage (for example one was skipped for 5246c1ccb5: https://github.com/JoinMarket-Org/joinmarket-clientserver/actions/runs/18861473464/job/53820509485 )

ACKs for top commit:
  kristapsk:
    cr utACK 9eaca78600

Tree-SHA512: 28c4b9b70b8bd27ef5729ff062c3062faf9954062085d126892f347e1ea430790a89dd46bef53e153b7880b6e0474769a34b1e383b90ec1e39892209388285da

.github/workflows/unittests.yml

@@ -7,6 +7,7 @@ jobs:
     name: python ${{ matrix.python-version }}, bitcoind ${{ matrix.bitcoind-version }} on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
+      fail-fast: false
       matrix:
         os: [macos-13, ubuntu-latest]
         python-version: ["3.9", "3.13"]