chore(ci): restrict Dgraph test to core packages only (#2242)

**Description**

This PR restricts the Dgraph CI workflow to only check core Dgraph
packages. The intent of this CI workflow is to immediately identify
badger@main compatibility issues with the main branch of Dgraph. Running
the entire Dgraph test suite is overkill -- this should immediately find
any badger incompatibilities with Dgraph.

.github/workflows/ci-dgraph-tests.yml

@@ -64,7 +64,7 @@ jobs:
           # move the binary
           cp dgraph/dgraph ~/go/bin/dgraph
           # run the tests
-          cd t; ./t
+          cd t; ./t --pkg=edgraph,posting,worker,query
           # clean up docker containers after test execution
           ./t -r
           # sleep