Change DeprecationWarning and PendingDeprecationWarning to UserWarning

[mariaschuld]

@antalszava noted that the deprecation warning does not show in common editors (despite begin raised and tested). I realised that other warnings in PL have stack level 2, so adapting it here.

[github-actions]

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Please edit .github/CHANGELOG.md with:

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[codecov]

Codecov Report

Merging #1211 (dfb0357) into master (beaf0a6) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1211   +/-   ##
=======================================
  Coverage   98.11%   98.11%           
=======================================
  Files         146      146           
  Lines       11056    11056           
=======================================
  Hits        10848    10848           
  Misses        208      208           

Impacted Files	Coverage Δ
pennylane/_qubit_device.py	98.50% <ø> (ø)
pennylane/devices/default_qubit_jax.py	94.36% <ø> (ø)
pennylane/qnode.py	98.67% <ø> (ø)
pennylane/templates/embeddings/amplitude.py	100.00% <ø> (ø)
pennylane/vqe/vqe.py	92.81% <ø> (ø)

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[antalszava]

Leaving a note here too. To get the warning show locally, I either had to:

1. add the warnings.simplefilter('always', DeprecationWarning) line so that deprecation warnings are raised or
2. change the type of the warning from DeprecationWarning.

Option 1. would impact the entire codebase, so not entirely sure about the other deprecation warnings we have in place 🤔 Are they suppressed by default?

[josh146]

What happens if we change all the DeprecationWarning warnings to PendingDeprecationWarning? Does that avoid the filtering?

[antalszava]

Unfortunately PendingDeprecationWarning doesn't work either :(

[josh146]

@mariaschuld @antalszava what is our next steps here? Is it to add our own warning filter system to PL, like other common packages do? It would be great to get this out ASAP since it is stopping users from seeing the deprecation warnings.

[antalszava]

@josh146 saw this just recently, I'll pick this up today!

[josh146]

Thanks for helping with this @antalszava! Were these all the current deprecation warnings in the codebase?

[antalszava]

Yep, was using sed to do a search and replace. Thought that it's sensible to change everywhere, though lmk if that's not something we'd like to go for.

[mariaschuld]

Thanks for finalising this!