[Investigation] Lengthy CI builds

Are you certain it's a bug?

[X] Yes, it looks like a bug

Are you using the latest plugin release?

[X] Yes, I'm using the latest plugin release

Is there an existing issue for this?

[X] I have searched existing issues, it hasn't been reported yet

Issue description

This is for my own bookkeeping, it looks like we have a bit of a regression on CI at the moment, where all the test runs take a very long time (or even timeout). In order to unblock release, I will temporarily turn off certain test runs and then gradually modernize the current CI test suite (which is quite outdated at the moment).

Service configuration (serverless.yml) content

N/A

Command name and used flags

N/A

Command output

N/A

Environment information

N/A

serverless / serverless-python-requirements

[Investigation] Lengthy CI builds #798