Elimate requires_grad=True warnings from device tests

[dime10]

Small PR to remove requires_grad=True warnings from the device tests in:

• tests/devices
• pennylane/devices/tests

These warnings were introduced in anticipation of Pennylane v0.20.0 making the default requires_grad=False for variational parameters.

[dime10]

[sc-11205]

[codecov]

Codecov Report

Merging #1913 (abc3eea) into master (9cf401d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1913   +/-   ##
=======================================
  Coverage   98.83%   98.83%           
=======================================
  Files         222      222           
  Lines       16979    16979           
=======================================
  Hits        16781    16781           
  Misses        198      198           

Impacted Files	Coverage Δ
pennylane/ops/qubit/non_parametric_ops.py	97.36% <ø> (ø)

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[albi3ro]

Thanks for this :)

Just needs a changelog entry and I'll approve.

[albi3ro]

:) Just the one spelling thing.