docker warnings in this project

[v1v]

3 warnings found (use docker --debug to expand):
--
  | - InvalidDefaultArgInFrom: Default value for ARG debian:${DEBIAN_VERSION} results in empty or invalid base image name (line 2)
  | - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 28)
  | - LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 29)

and

;t=1723240878886 => WARN: InvalidDefaultArgInFrom: Default value for ARG ${REPOSITORY}/golang-crossbuild:${VERSION}-base${TAG_EXTENSION} results in empty or invalid base  0.0s
bk;t=1723240879036 => WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 4)                                                                             0.0s
bk;t=1723240879036 => WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 39)                                                                            0.0s
bk;t=1723240879036 => WARN: FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 71)  

https://buildkite.com/elastic/golang-crossbuild/builds/444#01915219-283e-4703-9997-919f05eda82f/6-50
https://buildkite.com/elastic/golang-crossbuild/builds/446#019154e7-1840-4764-bab2-3f12b6165e2a/6-10