Fix variable usage in test-aot-compatibility script

[eerhardt]

Minor fix up of the powershell script.

Porting change from open-telemetry/opentelemetry-dotnet#5645.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.69%. Comparing base (71655ce) to head (bb87da6).
Report is 269 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1837      +/-   ##
==========================================
+ Coverage   73.91%   75.69%   +1.77%     
==========================================
  Files         267      300      +33     
  Lines        9615    11545    +1930     
==========================================
+ Hits         7107     8739    +1632     
- Misses       2508     2806     +298     

Flag	Coverage Δ
unittests-Exporter.Geneva	62.24% <ø> (?)
unittests-Exporter.OneCollector	89.72% <ø> (?)
unittests-Extensions	79.33% <ø> (?)
unittests-Instrumentation.AspNet	74.85% <ø> (?)
unittests-Instrumentation.AspNetCore	85.27% <ø> (?)
unittests-Instrumentation.EventCounters	76.36% <ø> (?)
unittests-Instrumentation.GrpcNetClient	79.61% <ø> (?)
unittests-Instrumentation.Http	81.79% <ø> (?)
unittests-Instrumentation.Owin	83.43% <ø> (?)
unittests-Instrumentation.Process	100.00% <ø> (?)
unittests-Instrumentation.Runtime	100.00% <ø> (?)
unittests-Instrumentation.SqlClient	90.90% <ø> (?)
unittests-Instrumentation.StackExchangeRedis	71.00% <ø> (?)
unittests-Instrumentation.Wcf	78.47% <ø> (?)
unittests-PersistentStorage	65.78% <ø> (?)
unittests-ResourceDetectors.Azure	81.53% <ø> (?)
unittests-Resources.Gcp	72.54% <ø> (?)
unittests-Resources.Host	52.87% <ø> (?)
unittests-Resources.Process	81.81% <ø> (?)
unittests-Resources.ProcessRuntime	72.91% <ø> (?)
unittests-Solution	80.17% <ø> (?)

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see 272 files with indirect coverage changes