v1.6.0-beta.1 CAPD arm64 image contains the test-extension binary. The issue has been resolved and the v1.6.0-rc.0 image has the correct binary again.
v1.5.3 test-extension arm64 & s390x images contain the CAPD binary. The issue has been resolved and the v1.5.4 images will have the correct binary again.
Best, Cluster API Release Lead on behalf of CAPI Release Team