ci: fix using tarantoolctl in tests

The problem is that on Ubuntu 22.04 luarocks v3 from the
`tarantool-common` package is installed, but tarantoolctl
from tarantool 1.10 uses luarocks v2.
See [1] for more details.

[1] tarantool/tarantool#5429 (comment)

Author: LeonidVas

.github/workflows/tests.yml

@@ -14,7 +14,7 @@ jobs:
     if: |
       github.event_name == 'push' ||
       github.event_name == 'pull_request' && github.event.pull_request.head.repo.owner.login != 'tarantool'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         tarantool-version: ["1.10", "2.8", "2.x-latest"]
@@ -128,7 +128,7 @@ jobs:
   tests-ee:
     if: |
       github.event_name == 'push'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         tests: ["other", "integration"]