fix: latest pytest version breaking tests

[hallvictoria]

Description

On 6/4, pytest released a new version == 8.2.2, which caused several of the E2E and unit tests to fail with an AssertionError "assert testcase is not None". This changes to install a compatible version of pytest. 7.4.4 is the latest version we can pin to, as the 8.* versions are not supported in python 3.7.

For example:

• E2E tests: https://github.com/Azure/azure-functions-python-worker/actions/runs/9413740604/job/25931135947
• Unit tests: https://github.com/Azure/azure-functions-python-worker/actions/runs/9397259034/job/25880092469

Fixes #

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• New Unit tests were added for the changes made and CI is passing.

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[YunchuWang]

nit: add broken pipeline link to this pr for easy tracking if needed in future