ci/appveyor: Build packages after tests were run

  Our scenarios test suite is not very stable on AppVeyor and builds can
  fail quite a lot before finally passing for no specific reason.
  This can prevent us from shipping a release while tests were passing
  on a previous commit with no code changes.

  Building packages in a flow step separate from tests ensures we can
  ship releases even when scenarios fail while still giving us the
  possibility to refrain from shipping the built package if some
  scenario fails for what looks to be a good reason.

Author: taratatach

.appveyor.yml

@@ -24,9 +24,12 @@ test_script:
   - ps: if ($env:BUILD_JOB -eq "short_tests") { yarn test:unit --timeout $env:MOCHA_TIMEOUT }
   - ps: if ($env:BUILD_JOB -eq "short_tests") { yarn test:integration --timeout $env:MOCHA_TIMEOUT }
   - ps: if ($env:BUILD_JOB -eq "scenarios_build") { yarn test:scenarios --timeout $env:MOCHA_TIMEOUT }
-  - ps: if ($env:BUILD_JOB -eq "scenarios_build") { yarn dist:all }
 
 on_failure:
   - node --version
   - npm --version
   - yarn --version
+
+on_finish:
+  - ps: if ($env:BUILD_JOB -eq "scenarios_build") { yarn dist:all }
+