oeqa/gitarchive: Fix git push URL parameter

oeqa/gitarchive: Fix git push URL parameter

The gitarchive() function takes a `push` parameter than can be either a
boolean or a string. But this parameter is then passed to
expand_tag_strings(), which clearly expect it to be a string if it is
defined. Split this in two arguments: a `push` boolean value and a
`push_remote` optional string.

Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>