CompatHelper: bump compat for "PDMats" to "0.11"

[github-actions]

This pull request changes the compat entry for the PDMats package from 0.9, 0.10 to 0.9, 0.10, 0.11.

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]

Codecov Report

Merging #13 (7f582b5) into master (160fc34) will decrease coverage by 2.10%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
- Coverage   66.66%   64.55%   -2.11%     
==========================================
  Files           3        3              
  Lines          87       79       -8     
==========================================
- Hits           58       51       -7     
+ Misses         29       28       -1     

Impacted Files	Coverage Δ
src/woodbury_pd_mat.jl	92.00% <0.00%> (-1.34%)	⬇️
src/psd_mat.jl	50.94% <0.00%> (-0.85%)	⬇️

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