Clone libakgl's other two submodules, and pin upload-artifact to v3

Two more gaps that only became visible once the errno fix let the jobs
run far enough to hit them.

akgl_build cloned six of libakgl's submodules and needs eight. libakgl
does not add_subdirectory deps/libccd or deps/clay -- their own
CMakeLists are unusable as subprojects -- it compiles them into itself,
so nothing declares them and configuration dies at
deps/libakgl/CMakeLists.txt:282 with "File
deps/libccd/src/ccd/config.h.cmake.in does not exist". deps/tg stays out:
nothing references it.

The X11 packages from the previous commit did their job -- SDL now
configures the lot: "X11 libraries: xcursor xdbe xfixes xinput2 xrandr
xscrnsaver xshape xsync xtest".

coverage passes its gate now (112/112, lines 94.1% against a 90 floor)
and failed on the upload instead. actions/upload-artifact@v4 bundles
@actions/artifact v2, whose isGhes() treats any GITHUB_SERVER_URL that is
not github.com as GitHub Enterprise Server and refuses outright. @v3 uses
the older artifact API, which Gitea 1.25.3 does implement. The step had
never had a file to upload before -- gcovr was never reached, so it
warned "No files were found" and passed -- which is why this surfaced
only now. Same class of accommodation as annotate_only on the junit
reporter.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -148,9 +148,21 @@ jobs:
             --fail-under-line 90
       # Publish even when the threshold gate fails, so the uncovered lines are
       # visible -- each one is a missing test.
+      #
+      # @v3, not @v4, and that is Gitea rather than preference. @v4 bundles
+      # @actions/artifact v2, whose isGhes() treats any GITHUB_SERVER_URL that is
+      # not github.com as GitHub Enterprise Server and refuses outright:
+      # "GHESNotSupportedError: @actions/artifact v2.0.0+, upload-artifact@v4+
+      # and download-artifact@v4+ are not currently supported on GHES". @v3 uses
+      # the older artifact API, which this forge does implement.
+      #
+      # This never showed before because the step had nothing to upload: gcovr
+      # was never reached, so the step warned "No files were found" and passed.
+      # Fixing the suite is what first gave it a real file to refuse. Same class
+      # of accommodation as the annotate_only flag on the junit reporter above.
       - name: upload coverage reports
         if: always()
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v3
         with:
           name: code-coverage
           path: build-coverage/coverage/
@@ -175,11 +187,23 @@ jobs:
       # embedded it takes a find_package path instead, so our CMakeLists declares
       # those targets first and needs the submodules present. Six of them, none
       # recursive. Filed upstream as libakgl API-gap item 5.
+      #
+      # Eight, not six: deps/libccd and deps/clay were missing and are not
+      # optional. libakgl does not add_subdirectory either of them -- their own
+      # CMakeLists are unusable as subprojects -- it compiles them into itself,
+      # so nothing declares them and configuration dies late with "File
+      # deps/libccd/src/ccd/config.h.cmake.in does not exist" at
+      # deps/libakgl/CMakeLists.txt:282. clay is the same shape one step later:
+      # deps/clay/clay.h is on the include path and installed.
+      #
+      # deps/tg is a real submodule of libakgl and is deliberately not here --
+      # nothing in its CMakeLists references it. libakerror and libakstdlib are
+      # skipped for the reason the checkout note above gives.
       - name: libakgl dependencies
         run: |
           git -C deps/libakgl submodule update --init \
             deps/SDL deps/SDL_image deps/SDL_mixer deps/SDL_ttf \
-            deps/jansson deps/semver
+            deps/jansson deps/semver deps/libccd deps/clay
       # libfreetype-dev and libharfbuzz-dev are load-bearing, not incidental.
       # SDL_ttf prefers the system copies -- it reports "Using system freetype
       # library" and links libfreetype.so.6 -- and without them it would reach