assemble releases on ubuntu runners

The assemble job only ran on Windows for the case-insensitive filesystem, which
the overlays no longer depend on. Checking out the ~93000 game data files is
most of what the job does, and ubuntu runners are quicker and cheaper at it.

Naming the executable has to be exact now: the artifact is named after the
matrix entry, which is lowercase, while the executable inside it is named after
the CMake target, which is the uppercased application. Only NTFS was making
those agree.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.github/workflows/release.yml

@@ -33,7 +33,7 @@ jobs:
           || github.event_name != 'workflow_dispatch'
              && ( ( github.repository == '1dot13/source' && github.ref_name == 'master' )
                   || startsWith(github.ref, 'refs/tags/v') ) }}
-    runs-on: windows-latest # required for case-insensitive filesystem handling
+    runs-on: ubuntu-latest
     # at least English has to work
     continue-on-error: ${{ matrix.language != 'English' }}
     strategy:
@@ -80,7 +80,7 @@ jobs:
           set -eux
           for APP in ja2 ja2mapeditor ja2ub ja2ubmapeditor
           do
-            mv artifacts/${APP}/${APP}.exe gamedir/${APP}.exe
+            mv artifacts/${APP}/${APP^^}.exe gamedir/${APP}.exe
           done
 
       - name: Create version information file