.github/workflows/build.yml: clear the gap workspace cache during tes…

…t-new

If GAP was upgraded, we will need to reset (i.e. delete) the existing GAP
workspace cache before running the doctests.

.github/workflows/build.yml

@@ -251,6 +251,7 @@ jobs:
         run: |
           export MAKE="make -j2 --output-sync=recurse" SAGE_NUM_THREADS=4
           # https://github.com/tj-actions/changed-files?tab=readme-ov-file#outputs-
+          rm -rf $HOME/.sage/gap
           ./sage -t --long --format github -p4 ${{ steps.changed-files.outputs.doctests_all_changed_files }}
         shell: sh .ci/docker-exec-script.sh BUILD /sage {0}