CI: Use ant 1.10.18

The shared workflow defaults to apache-ant-1.10.15, which is no longer on
downloads.apache.org, so setup-ant fails before anything is built.

Author: watmildon

.github/workflows/ant.yml

@@ -20,6 +20,8 @@ jobs:
     uses: JOSM/JOSMPluginAction/.github/workflows/ant.yml@v3
     with:
       java-version: 17
+      # The workflow default (1.10.15) is no longer on downloads.apache.org
+      ant-version: apache-ant-1.10.18
       josm-revision: ${{ matrix.josm-revision }}
       plugin-jar-name: 'mapwithai'
       perform-revision-tagging: ${{ matrix.josm-revision == 'r19067' && github.repository == 'JOSM/MapWithAI' && github.ref_type == 'branch' && github.ref_name == 'master' && github.event_name != 'schedule' && github.event_name != 'pull_request' }}