t: silence output from `test_create_repo()`

t: silence output from `test_create_repo()`

There are a couple users of `test_create_repo()` that use this function
outside of any test case. This function is nowadays only a thin wrapper
around `git init`, which by default prints a message to stdout that the
repository has been initialized. The resulting output may thus confuse
TAP parsers.

Refactor these users to instead create the repository in a "setup" test
case so that we don't explicitly have to silence them. There's one
exception in t1007: we use `push_repo()` and its `pop_repo()` equivalent
multiple times, so to reduce the noise introduced by this patch we
instead silence this invocation.

While at it, convert callsites to use git-init(1) directly as the
`test_create_repo()` function has been deprecated in f0d4d398e28
(test-lib: split up and deprecate test_create_repo(), 2021-05-10).

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>