Fix typo in the mappings file rendered during CI
Fix typo in the mappings file rendered during CI

In PR #758 we changed the AMI mappings keys to
linxuamd64/linuxarm64/windows. However, we left an older format
(linux_arm64/linux_amd64) in the version of the template rendered during
CI.

holmesjr/elastic-ci-stack-for-aws,buildkite/elastic-ci-stack-for-aws,holmesjr/elastic-ci-stack-for-aws