test: fix test breakage caused by external dependency update

[aaron-prindle]

Recently kaniko CI/CD tests started failing due to external dependency change. Tests are failing stating the ENV produced by kaniko differes from docker now although this failure occured not directly related to a kaniko PR and no kaniko logic related to this has changed recently. PR here attempts to fix this

log snippet

              		Diff: &integration.metaDiffResult{
            - 			Adds: []string{"Env: PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"},
            + 			Adds: []string{},
            - 			Dels: []string{"Env: "},
            + 			Dels: []string{},

full logs showing the test failure
https://github.com/GoogleContainerTools/kaniko/actions/runs/8177044948/job/22357785283

This test failure is not directly related to any kaniko PR but some external dependency change, either an external image our tests rely (busybox:latest) on changing or the docker on the Github Action Runner being updated in some form

By default kaniko adds the following to SCRATCH containers which I believe mirrors how docker works:

pkg/constants/constants.go
64:var ScratchEnvVars = []string{"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"}

This is the env shown when I run busybox:latest locally:

aprindle@aprindle-ssd ~/kaniko  [root-cause-test-issue]docker run -it  --entrypoint=sh busybox:latest
/ # 
/ # env
HOSTNAME=d12a084c5d2e
SHLVL=1
HOME=/root
TERM=xterm
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin # <-------------value as expected here
PWD=/

The fix is to add these ENV vars explicity in the two docker tests seeing issues for now as I believe this is not an issue with kaniko's logic IIUC

[JeromeJu]

Thanks @aaron-prindle , LGTM for the patch.