slack-15.0: fix private repo git config in docker build

[timvaillancourt]

Description

This PR should fix access issues in our Jenkins build due to using a Durability Policy in a private repo, and the Docker build being unprepared for this:

2024.05.22 19:42:46 #8 4.691 go: downloading github.com/mattn/go-colorable v0.1.6
2024.05.22 19:42:46 #8 4.694 go: downloading github.com/remyoudompheng/bigfft v0.0.0-20200410134404-eec4a21b6bb0
2024.05.22 19:42:46 #8 4.741 go: downloading github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd
2024.05.22 19:42:46 #8 4.741 go: downloading github.com/hashicorp/go-immutable-radix v1.1.0
2024.05.22 19:42:46 #8 4.805 go: downloading github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e
2024.05.22 19:42:47 #8 5.671 go/vt/vtctl/reparentutil/slack_cross_cell_shim.go:3:8: reading github.com/slackhq/vitess-addons/go.mod at revision v0.15.3: git ls-remote -q origin in /go/pkg/mod/cache/vcs/deddcb84177463a570ad3cac1ad9ff1e94bf4f985fbe6cc27416617e75330028: exit status 128:
2024.05.22 19:42:47 #8 5.671 	fatal: could not read Username for 'https://github.com/': terminal prompts disabled
2024.05.22 19:42:47 #8 5.671 Confirm the import path was entered correctly.
2024.05.22 19:42:47 #8 5.671 If this is a private repository, see https://golang.org/doc/faq#git_https for additional information.
2024.05.22 19:42:47 #8 5.674 make: *** [Makefile:85: build] Error 1
2024.05.22 19:42:48 #8 ERROR: process "/bin/sh -c make build" did not complete successfully: exit code: 2
2024.05.22 19:42:48 ------

This issue was introduced in #266 where I should have updated these Dockerfiles 🤦

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes