ci: Also set -Ddefault_library=static for Ubuntu

WrapDB's luajit can build both library types, defaulting (as usual) to
shared libraries.

Setting -Ddefault_library=static is not needed for the CI to work, but
users might refer to the CI for how to compile Aegisub locally, and
they'd probably want a statically linked luajit.

.github/workflows/ci.yml

@@ -43,25 +43,25 @@ jobs:
             name: Ubuntu 22 Debug,
             os: ubuntu-22.04,
             buildtype: debugoptimized,
-            args: ''
+            args: -Ddefault_library=static
           }
           - {
             name: Ubuntu 22 Release,
             os: ubuntu-22.04,
             buildtype: release,
-            args: ''
+            args: -Ddefault_library=static
           }
           - {
             name: Ubuntu 24 Debug,
             os: ubuntu-24.04,
             buildtype: debugoptimized,
-            args: ''
+            args: -Ddefault_library=static
           }
           - {
             name: Ubuntu 24 Release,
             os: ubuntu-24.04,
             buildtype: release,
-            args: ''
+            args: -Ddefault_library=static
           }
           - {
             name: macOS Debug,