ci: disable 'testpackage' linter in golangci

The 'testpackage' linter recommends "black box" testing, which prevents
testing internal/non-exported functions from being tested. We have tests
that *do* test non-exported functions and types.

Disabling the linter allows us to test non-exported types and functions.

Signed-off-by: Niels de Vos <ndevos@redhat.com>

scripts/golangci.yml.in

@@ -164,3 +164,4 @@ linters:
     - godox
     - wsl
     - funlen
+    - testpackage