Add workaround for test broken by Git security fix

The fix for this Git security issue [1] involved disabling the local
clone optimization when the repository contains symbolic links. The
security fix broke this particular test; this patch works around the
fix.

[1]: https://github.com/git/git/security/advisories/GHSA-3wp6-j8xr-qw85

test/tests/shim.bash

@@ -2,6 +2,7 @@ test_description='install shim works'
 . '../test-lib.bash'
 
 test_expect_success 'setup' '
+git config --global protocol.file.allow always
 cd ${DOTFILES}
 git init
 git submodule add ${BASEDIR} dotbot