fix_holonomic caching error

[iammosespaulr]

References to other Issues or PRs

Fixes #19222

Brief description of what is fixed or changed

Fixes a cache mismatch due to usingis instead of == in holonomic.py

Other comments

Release Notes

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#### References to other Issues or PRs
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Fixes #19222

#### Brief description of what is fixed or changed

Fixes a cache mismatch due to using`is` instead of `==` in `holonomic.py`

#### Other comments


#### Release Notes

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[iammosespaulr]

the tests pass now, @oscarbenjamin @jksuom

[jksuom]

There is another case a few lines earlier. Maybe that should be changed as well.

[codecov]

Codecov Report

Merging #19236 into master will increase coverage by 0.029%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master    #19236       +/-   ##
=============================================
+ Coverage   75.650%   75.680%   +0.029%     
=============================================
  Files          651       651               
  Lines       169488    169486        -2     
  Branches     40021     40021               
=============================================
+ Hits        128219    128268       +49     
+ Misses       35652     35604       -48     
+ Partials      5617      5614        -3     

[smichr]

@oscarbenjamin, this could be included in the 1.6 release.

[oscarbenjamin]

@oscarbenjamin, this could be included in the 1.6 release.

Yes, it could. To make that happen do this:

1. Leave this unmerged for now.
2. Open a new PR from the same branch but against the 1.6 branch - add the release note there.
3. I'll merge it into 1.6.
4. Remove the release note here and merge it into master.

[iammosespaulr]

@smichr @oscarbenjamin I've done this #19236 (comment)