[projmgr] Skip cbuild-run generation when target-set has only lib contexts

[grasci-arm]

Address ARM-software/vscode-cmsis-csolution#312

[github-actions]

Test Results

    3 files     21 suites   12m 56s ⏱️
  421 tests   421 ✅ 0 💤 0 ❌
1 263 runs  1 263 ✅ 0 💤 0 ❌

Results for commit 3274f12.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.63%. Comparing base (d210ea8) to head (3274f12).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
tools/projmgr/src/ProjMgr.cpp	0.00%	0 Missing and 1 partial ⚠️
tools/projmgr/test/src/ProjMgrUnitTests.cpp	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2199   +/-   ##
=======================================
  Coverage   66.62%   66.63%           
=======================================
  Files         181      181           
  Lines       38514    38521    +7     
  Branches    22581    22585    +4     
=======================================
+ Hits        25661    25668    +7     
  Misses       8086     8086           
  Partials     4767     4767           

Flag	Coverage Δ
projmgr-cov	80.76% <80.00%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
tools/projmgr/include/ProjMgrWorker.h	64.28% <ø> (ø)
tools/projmgr/src/ProjMgrWorker.cpp	87.84% <100.00%> (+0.04%)	⬆️
tools/projmgr/src/ProjMgr.cpp	80.37% <0.00%> (ø)
tools/projmgr/test/src/ProjMgrUnitTests.cpp	80.23% <75.00%> (-0.02%)	⬇️

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