ci: add Ubuntu Groovy (20.10) workflow again

Add the ubuntu_20_10.yml and ubuntu_20_10_aarch64.yml workflow files to
build Tarantool packages for x86_64 and aarch64 systems.

Actually, it was already added in 980d7676 (2.9.0-100-g980d7676b) in the
scope of #5824 and removed then in 19a161b5 (2.10.0-beta2-4-g19a161b5f)
and dc19be40 (2.10.0-beta2-5-gdc19be406).

But, eventually, it was decided to add this workflow again to release
Tarantool packages for Ubuntu Groovy as well.

Follows-up tarantool/tarantool#5824

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

(cherry picked from commit 47fbd24a)