bitbake: tests/fetch: Tweak to work on Fedora40

On Fedora40, "localhost" sometimes resolves to ::1 and sometimes to 127.0.0.1
and python only binds to one of the addresses, leading to test failures.

Use 127.0.0.1 explicitly to avoid problems of the name resolution, we're trying
to test things other than the host networking.

(Bitbake rev: 3147ebb0edcca8f7f850aabd86ef010ab593496f)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 9adc6da42618f41bf0d6b558d62b2f3c13bedd61)
Signed-off-by: Steve Sakoman <steve@sakoman.com>