gqltest: migrate repository text search

Created by: unknwon

Migrated following tests to dev/gqltest:

https://github.com/sourcegraph/sourcegraph/blob/5ce8ae587d734252af7d8ab439510a8fddb4f421/internal/cmd/search-integration-tester/search_tests.go#L18-L47

Easier to review by commit.

Part of #12143.