interpolate scratch_dir to avoid precompilation failure in 1.12

[lmiq]

Description

Interpolating the scratch_dir variable in the precompilation directive solves the precompilation failure observed in v1.12-beta1.

Attribution

• I am listed in .zenodo.json (see How to get acknowledged #3503)

Things to consider

• Does it work on log scales?
• Does it work in layouts?
• Does it work in recipes?
• Does it work with multiple series in one call?
• PR includes or updates tests?
• PR includes or updates documentation?

[lmiq]

I think it would be nice, if this is a good solution, to make a 1.40.13 release with this as soon as possible, because otherwise CI runs will fail for all packages in Julia 1.12 pre-releases that depend on Plots.jl (on extensions, for example).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.38%. Comparing base (fa65e7d) to head (ef43f16).
Report is 41 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5072      +/-   ##
==========================================
- Coverage   89.77%   89.38%   -0.39%     
==========================================
  Files          40       40              
  Lines        8780     8452     -328     
==========================================
- Hits         7882     7555     -327     
+ Misses        898      897       -1     

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[BeastyBlacksmith]

Thanks! Would be nice, if you also could port that to the v2 branch.