ci: fix arm build

[peninoule]

ARM local build fails with the following error:

ERROR: Skipping '//test/extensions...': no such package 'test/extensions...': BUILD file not found in any of the following directories. Add a BUILD file to a directory to mark it as a package.

With the additional /, the tests start

[solo-build-bot]

Waiting for approval from someone in the solo-io org to start testing.