CompatHelper: bump compat for SymbolicUtils to 0.20, (keep existing compat)

[github-actions[bot]]

This pull request changes the compat entry for the SymbolicUtils package from 0.17, 0.18, 0.19 to 0.17, 0.18, 0.19, 0.20. This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov[bot]]

Codecov Report

Merging #103 (2aaa47c) into main (9499c47) will decrease coverage by 95.81%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #103       +/-   ##
==========================================
- Coverage   95.81%   0.00%   -95.82%     
==========================================
  Files           5       5               
  Lines         287     287               
==========================================
- Hits          275       0      -275     
- Misses         12     287      +275     

Impacted Files	Coverage Δ
src/reactions.jl	0.00% <0.00%> (-99.06%)	:arrow_down:
src/events.jl	0.00% <0.00%> (-96.16%)	:arrow_down:
src/rules.jl	0.00% <0.00%> (-95.13%)	:arrow_down:
src/utils.jl	0.00% <0.00%> (-94.45%)	:arrow_down:
src/systems.jl	0.00% <0.00%> (-92.31%)	:arrow_down:

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[paulflang]

Deprecated by #104