ci: test stable branches with SDK

Workflow submodule_update now brings latest commits in stable branches
further to tarantool/sdk, where integration tests can run with other
enterprise products and modules.

In tarantool/tarantool-ee a pull request is still opened, so the
maintainers can merge it at any time.

In tarantool/sdk the test branches are named in the following pattern:
`TarantoolBot/test-ce-master`
`TarantoolBot/test-ce-2.10`
and so on. This pattern can be easily distinguished by workflows,
which run integration tests and alert developers on failures.
It is also consistent with branches with the same purpose of integration
testing, that are created by the sdk_test workflow:
`TarantoolBot/test-ce-{feature_branch_name}`

NO_DOC=CI
NO_TEST=CI
NO_CHANGELOG=CI

Resolves tarantool/sdk#355

(cherry picked from commit 60a2ee11)