Filter out cast warnings in cast tests (pyccel#1824)

Mac in particular is bad at handling warnings in pytest. pyccel#1762
introduced lots of warnings as it is testing casting between types. Such
behaviour often raises warnings in NumPy. This PR deactivates those
warnings for these specific tests thus speeding up the mac tests by ~x2

---------

Co-authored-by: Yaman Güçlü <[email protected]>

Author: EmilyBourne

CHANGELOG.md

@@ -30,6 +30,7 @@ All notable changes to this project will be documented in this file.
 ### Changed
 -   #1720 : functions with the `@inline` decorator are no longer exposed to Python in the shared library.
 -   #1720 : Error raised when incompatible arguments are passed to an `inlined` function is now fatal.
+-   \[TESTS\] Filter out cast warnings in cast tests.
 -   \[INTERNALS\] `FunctionDef` is annotated when it is called, or at the end of the `CodeBlock` if it is never called.
 -   \[INTERNALS\] `InlinedFunctionDef` is only annotated if it is called.
 -   \[INTERNALS\] Build `utilities.metaclasses.ArgumentSingleton` on the fly to ensure correct docstrings.