Merge #7075: ci: free disk space by removing /output folder when it's no longer needed

3c6da38 ci: free disk space by removing `/output` folder when it's no longer needed (UdjinM6)

Pull request description:

  ## Issue being fixed or feature implemented
  `/output` folder just sits there wasting disk space after `Build source` step:
  - multiprocess 0.6GB
  - ubsan 1.7GB
  - tsan 2.4GB
  - nowallet 2.6GB
  - arm-linux 2.7GB
  - linux64 and linux64_sqlite 3.3GB

  (NOTE: fuzz, mac and win64 don't produce anything in `/output` folder)

  ## What was done?
  Remove the folder at the end of `Build source` step. Also drop unused `BASE_OUTDIR` env var pointing to it from `Run unit tests` step to avoid confusion.

  ## How Has This Been Tested?
  https://github.com/UdjinM6/dash/actions/runs/20355332620

  ## Breaking Changes
  n/a

  ## Checklist:
  - [ ] I have performed a self-review of my own code
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have added or updated relevant unit/integration/functional/e2e tests
  - [ ] I have made corresponding changes to the documentation
  - [ ] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  kwvg:
    utACK 3c6da38
  PastaPastaPasta:
    utACK 3c6da38

Tree-SHA512: 6cf26e4c2934dade8bc9c93bee649ceb113e67181690fee2c2be97700c4f840a87058dd527a734128929b16dc2168585ef2d6aadfafde2be286ff425e957db78

Author: PastaPastaPasta

.github/workflows/build-src.yml

@@ -99,6 +99,8 @@ jobs:
           ./ci/dash/build_src.sh
           ccache -X 9
           ccache -c
+          du -hd0 "${BASE_OUTDIR}"
+          rm -rf "${BASE_OUTDIR}"
         shell: bash
 
       - name: Save ccache cache
@@ -121,7 +123,6 @@ jobs:
 
       - name: Run unit tests
         run: |
-          BASE_OUTDIR="/output"
           BUILD_TARGET="${{ inputs.build-target }}"
           source ./ci/dash/matrix.sh
           ./ci/dash/test_unittests.sh