Run tests on ubuntu-latest

Ubuntu 20.04 is no longer supported by GitHub runners.

Note that Tarantool 2.8 and Python 3.7 are too old and not available on
ubuntu-latest so they're removed from the test matrix.

Author: locker

.github/workflows/test.yml

@@ -8,13 +8,13 @@ jobs:
         github.event.pull_request.head.repo.full_name != github.repository ) &&
         ( github.repository == 'tarantool/test-run' )
 
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
 
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
-        tarantool-version: ['2.8', '2.10', '2.11']
+        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
+        tarantool-version: ['2.10', '2.11']
 
     steps:
     - uses: actions/checkout@v3