[Doc] note that not all unit tests pass on CPU platforms (#17554)

Signed-off-by: David Xia <[email protected]>

Author: davidxia

docs/source/contributing/overview.md

@@ -58,6 +58,12 @@ Therefore, we recommend developing with Python 3.12 to minimise the chance of yo
 Currently, the repository is not fully checked by `mypy`.
 :::
 
+:::{note}
+Currently, not all unit tests pass when run on CPU platforms. If you don't have access to a GPU
+platform to run unit tests locally, rely on the continuous integration system to run the tests for
+now.
+:::
+
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