Challenge 'Refactoring To Use a Pure Function' does not use solution implementation from previous challenge

[svenvanderburg]

In episode 3.4 we introduce a class-based solution for loading in csv files in analyse_data(): https://carpentries-incubator.github.io/python-intermediate-development/33-code-decoupling-abstractions/index.html#solution-1

In the later solution we still use the old implementation, whereas students at that point will have the class-based implementation of analyse_date() https://carpentries-incubator.github.io/python-intermediate-development/34-code-refactoring/index.html#exercise-refactoring-to-use-a-pure-function

[svenvanderburg]

Proposed fix: https://github.com/esciencecenter-digital-skills/python-intermediate-development-gitlab/pull/8/commits/9a1bbec1bb1ba42ed0bae3499be3ca6d8c1aeed0

In addition: https://github.com/esciencecenter-digital-skills/python-intermediate-development-gitlab/pull/8/commits/8020659c983947c150dfcfb98fbfb24f485eb8c4 to also make 'Exercise: Write Regression Tests' to use the mocked data source