rewrite regex to silence deprecation warning

[jimregan]

What does this PR do ?

Add a one line overview of what this PR aims to accomplish.

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• [ ] Remove import guards (try import: ... except: ...) if not already done.
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• [ ] New Feature
• [ ] Bugfix
• [ ] Documentation
• [ ] Test

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[jimregan]

@ekmb This should be an uncontroversial change

[ekmb]

@ekmb This should be an uncontroversial change

LGTM, thanks!