Update v2 condition table targetValue validation

[dweindl]

After PEtab-dev/PEtab#645, any condition that is used as a first condition cannot refer to any symbols other then the parameters listed in the parameter table, or `time'.

Closes #424.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 77.77778% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.60%. Comparing base (876c781) to head (a00d04f).

Files with missing lines	Patch %	Lines
petab/v2/lint.py	76.92%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #427      +/-   ##
==========================================
+ Coverage   74.59%   74.60%   +0.01%     
==========================================
  Files          62       62              
  Lines        6735     6762      +27     
  Branches     1188     1196       +8     
==========================================
+ Hits         5024     5045      +21     
- Misses       1256     1259       +3     
- Partials      455      458       +3     

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