CI: fetch Proxifier LSP from a source we control

[belm0]

Closes #1938

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (a10f94b) 99.68% compared to head (80a4f89) 99.68%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1946   +/-   ##
=======================================
  Coverage   99.68%   99.68%           
=======================================
  Files         117      117           
  Lines       17546    17546           
  Branches     3152     3152           
=======================================
  Hits        17490    17490           
  Misses         38       38           
  Partials       18       18           

[njsmith]

Weirdly, this seems to be consistently failing. I don't know why, since it looks like it should be doing the same thing as our current system...