Use assertRaisesRegex instead of assertRaisesRegexp for Python 3.11 compatibility

[tirkarthi]

Code PR

The deprecated aliases were removed in Python 3.11 in python/cpython#28268 . So this PR replaces assertRaisesRegexp with assertRaisesRegex for Python 3.11 compatibility.

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Command to identify deprecated aliases :

 rg -t py 'assertEquals|assertNotEquals|assertAlmostEquals|assertNotAlmostEquals|assertRegexpMatches|assertNotRegexpMatches|assertRaisesRegexp|failUnlessEqual|failIfEqual|failUnlessAlmostEqual|failUnless|failUnlessRaises|failIf|assertDictContainsSubset|_TextTestResult' 

[tirkarthi]

I am not sure of the docs build error in CI

[nicolaskruchten]

Thanks for this!