Add retry logic to `_fetch_ref` in `RemoteGitRepository`

Miroslav Vadkertirequested to merge
add-fetch-ref-retries into main

_fetch_ref previously failed immediately on transient errors (e.g. HTTP 429 rate limiting) without any retries. This caused test jobs to fail when GitLab temporarily throttled git fetch requests.

Wrap git fetch in gluetool.utils.wait() with configurable fetch_timeout and fetch_tick parameters, matching the retry pattern already used by _do_clone. Thread timeout/tick values through _checkout_ref and _merge from clone().

Slack discussion: https://redhat-internal.slack.com/archives/C03BRN71JAF/p1777293385580169

Assisted-by: Claude Code

Signed-off-by: Miroslav Vadkerti mvadkert@redhat.com

Edited by Miroslav Vadkerti

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