fix(downloader): qdt_plugins_to_copy was not created in force mode

[Guts]

When force: true in plugins downloader job, it was failing because of unbound locale var:

2024-09-04 10:03:43||ERROR||bouncer||exit_cli_error||43||cannot access local variable 'qdt_plugins_to_copy' where it 
is not associated with a value
Traceback (most recent call last):
  File "qgis_deployment_toolbelt\commands\deployment.py", line 207, in run
  File "qgis_deployment_toolbelt\jobs\job_plugins_downloader.py", line 120, in run
UnboundLocalError: cannot access local variable 'qdt_plugins_to_copy' where it is not associated with a value

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 70.52%. Comparing base (58ba890) to head (6724399).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...deployment_toolbelt/jobs/job_plugins_downloader.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #551      +/-   ##
==========================================
- Coverage   70.55%   70.52%   -0.03%     
==========================================
  Files          47       47              
  Lines        3124     3125       +1     
  Branches      669      669              
==========================================
  Hits         2204     2204              
- Misses        726      727       +1     
  Partials      194      194              

Flag	Coverage Δ
unittests	69.95% <0.00%> (-0.03%)	⬇️

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

Files with missing lines	Coverage Δ
...deployment_toolbelt/jobs/job_plugins_downloader.py	50.37% <0.00%> (-0.39%)	⬇️