Build native_mixed on windows

Xapian build with meson is static only.
This is mainly due to missing "ddl export" or ".def" file.

Autotool buildsystem seems to handle that automatically but not meson.
See https://github.com/mesonbuild/meson/issues/2132 about meson
supporting this.

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: windows-latest
     env:
       OS_NAME: windows
-      COMPILE_CONFIG: native_dyn
+      COMPILE_CONFIG: native_mixed
       HOME: 'C:\\Users\\runneradmin'
     steps:
     - name: Checkout code