Treat .bin files as binary in git. (#224)

I think this will help if the file contents change, preventing git from
trying to merge files as text. I _hoped_ this would also show the files
as binary, but that isn't working:
* Correctly binary:
https://github.com/nod-ai/SHARK-TestSuite/blob/main/iree_tests/onnx/node/generated/test_abs/output_0.npy
* Incorrectly text:
https://github.com/nod-ai/SHARK-TestSuite/blob/main/iree_tests/onnx/node/generated/test_abs/output_0.bin

We're already saving those files as binary, so something in the file
extensions might be special cased ¯\\\_(ツ)\_/¯

iree_tests/.gitattributes

@@ -1,2 +1,6 @@
 *.irpa filter=lfs diff=lfs merge=lfs -text
 *.mlirbc filter=lfs diff=lfs merge=lfs -text
+
+# Ignore diffs and treat as binary in Git and on GitHub.
+*.bin -diff
+*.bin binary linguist-generated