testing/gdcm: disable on armv7 & x86

unfortunate but to unlock the builders, here are the build logs:

• https://build.alpinelinux.org/buildlogs/build-edge-armv7/testing/gdcm/gdcm-3.0.23-r2.log
• https://build.alpinelinux.org/buildlogs/build-edge-x86/testing/gdcm/gdcm-3.0.23-r2.log