chore: add tparallel linter (#88)

Add the tparallel linter, which checks that subtests of a parallel
test also run in parallel.

.golangci.yml

@@ -241,6 +241,7 @@ linters:
     - staticcheck
     - structcheck
     - tenv
+    - tparallel
     - typecheck
     - unconvert
     - unused

database/pubsub_memory_test.go

@@ -14,6 +14,8 @@ func TestPubsubMemory(t *testing.T) {
 	t.Parallel()
 
 	t.Run("Memory", func(t *testing.T) {
+		t.Parallel()
+
 		pubsub := database.NewPubsubInMemory()
 		event := "test"
 		data := "testing"