don't close file handles in protoype dataset tests (#4963)

* don't close file handles in protoype dataset tests

* remove file closing from decoder
Co-authored-by: Francisco Massa <fvsmassa@gmail.com>

test/test_prototype_builtin_datasets.py

@@ -10,10 +10,7 @@ from torchvision.prototype.utils._internal import sequence_to_str
 
 
 def to_bytes(file):
-    try:
     return file.read()
-    finally:
-        file.close()
 
 
 def dataset_parametrization(*names, decoder=to_bytes):

torchvision/prototype/datasets/decoder.py

@@ -13,7 +13,4 @@ def raw(buffer: io.IOBase) -> torch.Tensor:
 
 
 def pil(buffer: io.IOBase) -> features.Image:
-    try:
     return features.Image(pil_to_tensor(PIL.Image.open(buffer)))
-    finally:
-        buffer.close()