tests: Stabilize the TestNotationCopyBundle test

For some unknown reason sometimes the copied bundle is already present in
the registry. It is safe to overwrite it, as the signature is unique to
the bundle, at the test will fail it is not the correct image.

Signed-off-by: Kim Christensen <kimworking@gmail.com>

tests/integration/signing_test.go

@@ -202,7 +202,7 @@ func TestNotationCopyBundle(t *testing.T) {
 	require.NoError(t, err, "Publish failed")
 
 	_, output, err = testr.RunPorterWith(func(pc *shx.PreparedCommand) {
-		pc.Args("copy", "--insecure-registry", "--sign-bundle", "--source", ref.String(), "--destination", copiedRef.String())
+		pc.Args("copy", "--insecure-registry", "--sign-bundle", "--source", ref.String(), "--destination", copiedRef.String(), "--force")
 	})
 	require.NoError(t, err, "Copy failed")