fix for cust sys packages path

[hallvictoria]

Description

Changes in worker and constants to fix "Customer packages not in sys path." warning log being hit.

Fixes #

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PR information

• The title of the PR is clear and informative.
• There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• If applicable, the PR references the bug/issue that it fixes in the description.
• New Unit tests were added for the changes made and CI is passing.

Quality of Code and Contribution Guidelines

• I have read the contribution guidelines.

[codecov]

Codecov Report

Merging #1335 (baf4464) into dev (5909387) will decrease coverage by 53.63%.
The diff coverage is 50.00%.

❗ Current head baf4464 differs from pull request most recent head fc16528. Consider uploading reports for the commit fc16528 to get more accurate results

@@             Coverage Diff             @@
##              dev    #1335       +/-   ##
===========================================
- Coverage   85.73%   32.11%   -53.63%     
===========================================
  Files          34       34               
  Lines        1942     1940        -2     
  Branches      367      367               
===========================================
- Hits         1665      623     -1042     
- Misses        210     1316     +1106     
+ Partials       67        1       -66     

Flag	Coverage Δ
unittests	32.11% <50.00%> (-53.58%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
azure_functions_worker/constants.py	100.00% <100.00%> (ø)
azure_functions_worker/dispatcher.py	19.04% <0.00%> (-69.68%)	⬇️

... and 23 files with indirect coverage changes