Change spree_default_credit_card_deperecated cop severity to warning

[safafa]

Description

We need to update this cop severity to a warning as mentioned in this issue

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Severity:

• - info
• - refactor
• - convention (default)
• - warning
• - error
• - fatal

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Wrong Code

 user.default_credit_card

Correct Code

 user.wallet.default_wallet_payment_source

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Solidus PR Link: # Replace with link to Solidus PR where the change has been made.

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Before submitting the PR make sure the following are checked:

• The PR relates to only one cop with a clear title and description.
• Feature branch is up-to-date with main (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran and ensured all tests are passing on a development environment.
• If this is a new cop, added an entry for the cop on /config/default.yml
• Updated Changelog

[MassimilianoLattanzio]

LGTM.

Just make sure you remember to fix the version number after other PRs are merged.