Correct ARMv8 to aarch64 in Jenkins

Found as a part of https://github.com/AdoptOpenJDK/openjdk-infrastructure/issues/1716#issuecomment-755202080

As suggested by @sxa (https://github.com/AdoptOpenJDK/openjdk-infrastructure/pull/1806#pullrequestreview-562539987), we should change the Jenkins name of the following machines, so they match the inventory.yml, i.e. remove the `l` from `armv(7|8)l`:

- [ ] build-packet-ubuntu1804-armv8l-1
- [ ] docker-scaleway-ubuntu1604-armv7l-1

Should just be a case of changing their names, and restarting the Jenkins agent.

Compare the Jenkins names for build-packet-ubuntu1804-armv8l-1 and docker-scaleway-ubuntu1604-armv7l-1 with inventory.yml. Update each name to use aarch64-compatible naming without the extra l, restart the Jenkins agents, and verify that the names match the inventory.

Written by the indexing model from the issue text.