oeqa/utils/gitarchive: fix tag pattern searching

oeqa/utils/gitarchive: fix tag pattern searching

Whenever we ask gitarchive to search for tags, we can provide it with a
pattern (containing glob patterns). However, when searching for example for
tags matching branch master-next, it can find more tags which does not
correspond exactly to branch master-next (e.g. abelloni/master-next tags
will match).

Prevent those additional tags from being fetched by gitarchive by using a
more specific pattern: prefix user-provided pattern with "refs/tags"

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>