make WOODPECKER_MIGRATIONS_ALLOW_LONG have an actuall effect (#2251)

close #2079

as we sett the global vars **after** migrations we did never had a
chance to propagate a **true** in WOODPECKER_MIGRATIONS_ALLOW_LONG to
the migrations ...

---------

Co-authored-by: qwerty287 <80460567+qwerty287@users.noreply.github.com>

cmd/server/setup.go

@@ -52,6 +52,8 @@ import (
 )
 
 func setupStore(c *cli.Context) (store.Store, error) {
+	// TODO: find a better way than global var to pass down to allow long migrations
+	server.Config.Server.Migrations.AllowLong = c.Bool("migrations-allow-long")
 	datasource := c.String("datasource")
 	driver := c.String("driver")
 	xorm := store.XORM{