Replaces deprecated tf.test.is_gpu_available.

This avoids a potential bug triggered by the unit test.

PiperOrigin-RevId: 281405747
Change-Id: I1162443f6a32f7bde319873466833a94d0f3180a

Author: Johannes Ball?

tensorflow_compression/python/layers/signal_conv_test.py

@@ -222,7 +222,7 @@ def is_implemented(self, batch, input_support, channels, filters,
   def data_formats(self):
     # On CPU, many ops don't support the channels first data format. Hence, if
     # no GPU is available, we skip these tests.
-    if tf.test.is_gpu_available(cuda_only=True):
+    if tf.config.experimental.list_physical_devices("GPU"):
       return ("channels_first", "channels_last")
     else:
       return ("channels_last",)