Update QA issue template
Notes that devs are not expected to work overtime. Also notes that testing can be done even after the deadline.
Both points have come up before (e.g., https://gitlab.com/gitlab-org/release/framework/issues/246), usually in retrospectives. See also: https://gitlab.com/gitlab-org/release/framework/issues/345#note_184865173
Edited by Mark Lapierre