tests: don't use 'file://...' URIs for testing git downloads.

While 'url-fetch*' in (guix download) special-cases these URIs, 'git-fetch'
does not.  Consequently, the recent changes to (guix scripts perform-download)
that disallow these URIs cause tests that use builtin:git-download to fail.

* guix/tests/git.scm (serve-git-repository, call-with-served-git-repository):
  new procedures.
  (with-served-git-repository, with-served-temporary-git-repository): new
  syntax.
* .dir-locals.el (scheme-mode): add indentation information for
  'with-served-git-repository'.
* tests/builders.scm ("git-fetch, file URI"): use git:// URI with
  'with-served-temporary-git-repository'.
* tests/derivations.scm ("'git-download' build-in builder, invalid hash",
  "'git-download' built-in builder, invalid commit", "'git-download' built-in
  builder, not found"): same.
  ("'git-download' built-in builder"): same, and use a nonce in the repo
  contents so that success isn't cached.

Change-Id: Id3e1233bb74d5987faf89c4341e1d37f09c77c80
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

0 files changed, 0 insertions, 0 deletions