Skip TestDeploy/Dockerfile in short mode to avoid timeout

The deploy test group takes close to 15 minutes total in CI.
Adding this test (which includes a 10-second release command + health
checks + BuildKit build) pushes the suite over the 15-minute timeout.

Since we already have comprehensive BuildKit deploy coverage from:
- TestDeployNodeApp/With_BuildKit
- TestFlyDeploy_Dockerfile
- TestFlyDeploy_DeployMachinesCheck
- All other deploy tests with --buildkit flag

...this test is redundant in CI short mode and can run on master only.

Author: mattp-fly

test/preflight/fly_deploy_test.go

@@ -456,6 +456,9 @@ func TestDeploy(t *testing.T) {
 		testDeploy(t, filepath.Join(testlib.RepositoryRoot(), "test", "preflight", "fixtures", "example-buildpack"), "--depot")
 	})
 	t.Run("Dockerfile", func(t *testing.T) {
+		if testing.Short() {
+			t.Skip("Skipping in short mode: test suite approaches 15m timeout with this test included")
+		}
 		t.Parallel()
 		// Dockerfiles explicitly use BuildKit with remote building
 		testDeploy(t, filepath.Join(testlib.RepositoryRoot(), "test", "preflight", "fixtures", "example"), "--buildkit --remote-only")