ignore nested pkgs in GOTEST_PKGS_EXCLUDE

This fixes a bug where some packages tests run twice in CI, because they
are subpackages of ones with dedicated jobs.  For example, notice
`client/allocrunner` tests ran in `test-client`[1] and `test-other`[2] despite
them being in the same workflow[3].

[1] https://circleci.com/gh/hashicorp/nomad/5262
[2] https://circleci.com/gh/hashicorp/nomad/5261
[3] https://circleci.com/workflow-run/ee7a9167-8fc7-49a5-897c-6c967e966014

GNUmakefile

@@ -13,7 +13,7 @@ GO_TEST_CMD = $(if $(shell which gotestsum),gotestsum --,go test)
 ifeq ($(origin GOTEST_PKGS_EXCLUDE), undefined)
 GOTEST_PKGS ?= "./..."
 else
-GOTEST_PKGS=$(shell go list ./... | sed 's/github.com\/hashicorp\/nomad/./' | egrep -v "^($(GOTEST_PKGS_EXCLUDE))$$")
+GOTEST_PKGS=$(shell go list ./... | sed 's/github.com\/hashicorp\/nomad/./' | egrep -v "^($(GOTEST_PKGS_EXCLUDE))(/.*)?$$")
 endif
 
 default: help