Fix syntax warning from is with a literal

[josephleekl]

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---

Context:
This PR added two instances of if tape_return_type is "state" in _adjoint_jacobian_base.py , that introduces python SyntaxWarning, e.g. :

_adjoint_jacobian_base.py:197: SyntaxWarning: "is" with a literal. Did you mean "=="?
  if tape_return_type is "state":

which is also observed in CI logs during testing (e.g. here )

Description of the Change:
This PR changes is to ==.

Benefits:
No more syntax warning - equivalent test here

Possible Drawbacks:

Related GitHub Issues:

[sc-85337]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.98%. Comparing base (d9d011e) to head (40b48fd).
Report is 1 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (d9d011e) and HEAD (40b48fd). Click for more details.

HEAD has 29 uploads less than BASE

Flag	BASE (d9d011e)	HEAD (40b48fd)
	35	6

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #1070       +/-   ##
===========================================
- Coverage   98.01%   63.98%   -34.04%     
===========================================
  Files         233       28      -205     
  Lines       39881     2610    -37271     
===========================================
- Hits        39090     1670    -37420     
- Misses        791      940      +149     

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[LuisAlfredoNu]

Thank you @josephleekl
for solving the warning message

[maliasadi]

🙌