[DEFECT] Documentation is failing to build on MacOS

Defect Description

When running make_docs.sh in the HERON/doc directory, the documentation fails to build and instead yields the following stack trace.

What did you expect to see happen?

The documentation should have built and yielded a pdf in an adjacent directory.

What did you see instead?

Building manuals ...
... building in user_manual...
Traceback (most recent call last):
  File "script/generate_user_manual.py", line 9, in <module>
    import collect_tex
  File "/Users/grifaa/Documents/projects/HERON/doc/user_manual/script/collect_tex.py", line 15, in <module>
    import Cases, Components, Placeholders
  File "/Users/grifaa/Documents/projects/HERON/src/Cases.py", line 15, in <module>
    from HERON.src.base import Base
ModuleNotFoundError: No module named 'HERON'
make: *** [populate] Error 1
... ... failed to make docs in user_manual

Do you have a suggested fix for the development team?

Fix the import in the generate_user_manual.py file.

Describe how to Reproduce Steps to reproduce the behavior:

Change to directory HERON/doc
run make_docs.sh

Screenshots and Input Files Please attach the input file(s) that generate this error. The simpler the input, the faster we can find the issue.

Platform (please complete the following information):

OS: macOS
Version: 12.4
Dependencies Installation: CONDA

For Change Control Board: Issue Review

This review should occur before any development is performed as a response to this issue.

[ x] 1. Is it tagged with a type: defect or task?
[ x] 2. Is it tagged with a priority: critical, normal or minor?
[ x] 3. If it will impact requirements or requirements tests, is it tagged with requirements?
[ x] 4. If it is a defect, can it cause wrong results for users? If so an email needs to be sent to the users.
[ x] 5. Is a rationale provided? (Such as explaining why the improvement is needed or why current code is wrong.)

For Change Control Board: Issue Closure

This review should occur when the issue is imminently going to be closed.

[x] 1. If the issue is a defect, is the defect fixed?
[x] 2. If the issue is a defect, is the defect tested for in the regression test system? (If not explain why not.)
[x] 3. If the issue can impact users, has an email to the users group been written (the email should specify if the defect impacts stable or master)?
[x] 4. If the issue is a defect, does it impact the latest release branch? If yes, is there any issue tagged with release (create if needed)?
[x] 5. If the issue is being closed without a pull request, has an explanation of why it is being closed been provided?

idaholab / HERON