Git submodule tests started failing after security patch

[dcharkes]

Tests started failing because of the use of https://github.blog/2022-10-18-git-security-vulnerabilities-announced/#cve-2022-39253

❌ test/lish/archives_and_uploads_a_package_test.dart: with an empty Git submodule (failed)
  Git error. Command: `git submodule add ../empty empty`
  stdout: 
  stderr: Cloning into 'C:/Users/runneradmin/AppData/Local/Temp/dart_test_25e6b504/myapp/empty'...
  fatal: transport 'file' not allowed
  fatal: clone of 'C:/Users/runneradmin/AppData/Local/Temp/dart_test_25e6b504/empty' into submodule path 'C:/Users/runneradmin/AppData/Local/Temp/dart_test_25e6b504/myapp/empty' failed
  exit code: 128
  package:pub/src/git.dart 65:7                             run
  ===== asynchronous gap ===========================
  test\lish\archives_and_uploads_a_package_test.dart 105:5  main.<fn>

❌ test/package_list_files_test.dart: with git with a submodule respects its .gitignore with useGitIgnore (failed)
  Git error. Command: `git submodule add ../submodule`
  stdout: 
  stderr: Cloning into '/tmp/dart_test_IEEKIJ/myapp/submodule'...
  fatal: transport 'file' not allowed
  fatal: clone of '/tmp/dart_test_IEEKIJ/submodule' into submodule path '/tmp/dart_test_IEEKIJ/myapp/submodule' failed
  exit code: 128
  package:pub/src/git.dart 65:7            run
  ===== asynchronous gap ===========================
  test/package_list_files_test.dart 279:9  main.<fn>.<fn>.<fn>

Fails on #3613 on all 3 OSes.

cc @sigurdm @jonasfj

[vielmetti]

This is almost certainly CVE-2022-39253 which prompted changes in git
due to security problems identified.

You may find this issue summary useful with an account of some workarounds
done by other projects.

https://vielmetti.typepad.com/logbook/2022/10/git-security-fixes-lead-to-fatal-transport-file-not-allowed-error-in-ci-systems-cve-2022-39253.html

[jglick]

https://bugs.launchpad.net/ubuntu/+source/git/+bug/1993586

[sigurdm]

We fixed this in #3633