Test suite: Don't assume that julia is in the PATH

[DilumAluthge]

The PkgEval.jl test suite runs this package's tests: https://github.com/JuliaCI/PkgEval.jl/blob/524847dc78c801a51a16ae7e747ebe19f8fc30a4/test/runtests.jl#L249-L249

Currently, PkgEval.jl CI is broken (log) with:

functions defined with `@timeit` macro generate code coverage: Error During Test at /home/pkgeval/.julia/packages/TimerOutputs/L5q5K/test/test_coverage.jl:9
  Got exception outside of a @test
  IOError: could not spawn `julia --startup-file=no --project=/home/pkgeval/.julia/packages/TimerOutputs/L5q5K --check-bounds=yes --code-coverage /home/pkgeval/.julia/packages/TimerOutputs/L5q5K/test/coverage_script.jl`: no such file or directory (ENOENT)
  Stacktrace:

My guess is that julia is not in the PATH inside the container created by PkgEval.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.62%. Comparing base (ada4b6c) to head (b4d3f28).
⚠️ Report is 24 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #202      +/-   ##
==========================================
+ Coverage   84.82%   94.62%   +9.79%     
==========================================
  Files           5        6       +1     
  Lines         323      484     +161     
==========================================
+ Hits          274      458     +184     
+ Misses         49       26      -23     

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[DilumAluthge]

Bump @KristofferC

cc: @maleadt