(And v9 later on to v10.)

When v9/v10 were added, making v8 automatically upgrade was deferred
"for a few months" to prevent interoperability problems if users also
have an old version of git-annex. Of course that could still be the
case, but there has been a good amount of time and this can't be put off
forever.

Allow setting annex.autoupgraderepository to false to avoid this upgrade.
Previously, that only prevented upgrades from no longer supported git-annex
versions, but v8 is still supported, and users may want to keep on v8 to
interoperate with an old git-annex version.

Sponsored-by: Boyd Stephen Smith Jr. on Patreon