Replace DoesNotExist with NoTangent

[devmotion]

Tests pass successfully locally with this PR.

[devmotion]

@oxinabox should one update the lower bounds of ChainRulesCore and/or ChainRulesTestUtils? I lost a bit track of when the different deprecations were introduced and removed.

[oxinabox]

Oops I missed this in #319

Why didn't CI fail there?

should one update the lower bounds of ChainRulesCore and/or ChainRulesTestUtils?

No, I updated them in #319.
At least the ones for ChainRulesCore are correct for this.

[devmotion]

Why didn't CI fail there?

Because tests used ChainRulesCore 0.9.45 which only deprecates DoesNotExist: e.g., https://github.com/JuliaMath/SpecialFunctions.jl/runs/2718082508#step:6:97

[devmotion]

Tests on master and in other PRs use ChainRulesCore 0.10 in which DoesNotExist is not defined anymore.

[giordano]

I take this is good to go? I'm going to merge as soon as CI finishes

[devmotion]

Can you also make a new release? I already updated the version number.

[codecov]

Codecov Report

Merging #327 (101f88f) into master (04ae807) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #327      +/-   ##
==========================================
+ Coverage   92.70%   92.74%   +0.03%     
==========================================
  Files          12       12              
  Lines        2645     2645              
==========================================
+ Hits         2452     2453       +1     
+ Misses        193      192       -1     

Flag	Coverage Δ
unittests	92.74% <100.00%> (+0.03%)	⬆️

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Impacted Files	Coverage Δ
src/chainrules.jl	100.00% <100.00%> (ø)
src/beta_inc.jl	90.99% <0.00%> (+0.15%)	⬆️

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[oxinabox]

Tests on master and in other PRs use ChainRulesCore 0.10 in which DoesNotExist is not defined anymore.

Bother. I thought I checked that it actually updated.
I wonder why it didn't.
Given nothing has changed in Compat for this PR and now it is updating.