test: move context to after db creation (#21224)

Closes  https://github.com/coder/internal/issues/1040

We move the context to just before it is used to avoid the scenario
where NewDB takes a while to spin up and runs up the context to the
deadline.

coderd/database/querier_test.go

@@ -6082,8 +6082,6 @@ func TestGetWorkspaceAgentsByParentID(t *testing.T) {
 	t.Run("NilParentDoesNotReturnAllParentAgents", func(t *testing.T) {
 		t.Parallel()
 
-		ctx := testutil.Context(t, testutil.WaitShort)
-
 		// Given: A workspace agent
 		db, _ := dbtestutil.NewDB(t)
 		org := dbgen.Organization(t, db, database.Organization{})
@@ -6098,6 +6096,8 @@ func TestGetWorkspaceAgentsByParentID(t *testing.T) {
 			ResourceID: resource.ID,
 		})
 
+		ctx := testutil.Context(t, testutil.WaitShort)
+
 		// When: We attempt to select agents with a null parent id
 		agents, err := db.GetWorkspaceAgentsByParentID(ctx, uuid.Nil)
 		require.NoError(t, err)