[issue40773] DOC: Fix rendering for 'retval' on the pdb page

[Chenyoo Hao]

Change by Chenyoo Hao <solitaire2312 at gmail.com>:


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pull_requests: +20246
pull_request: https://github.com/python/cpython/pull/21080

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40773>
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