Fix deactivate_unsupported_payment_methods name in error message

[kennyadsl]

In the doc printed when it's needed, we had a typo, probably due to some back and forth on the PR that introduced the change.

See #3837

Summary

Checklist

Check out our PR guidelines for more details.

The following are mandatory for all PRs:

• I have written a thorough PR description.
• I have kept my commits small and atomic.
• I have used clear, explanatory commit messages.

The following are not always needed:

• 📖 I have updated the README to account for my changes.
• 📑 I have documented new code with YARD.
• 🛣️ I have opened a PR to update the guides.
• ✅ I have added automated tests to cover my changes.
• 📸 I have attached screenshots to demo visual changes.

[codecov]

Codecov Report

Merging #5458 (f0bd4c6) into main (d479d6a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #5458   +/-   ##
=======================================
  Coverage   88.91%   88.91%           
=======================================
  Files         614      614           
  Lines       14829    14829           
=======================================
  Hits        13185    13185           
  Misses       1644     1644           

Files	Coverage Δ
core/app/models/spree/payment_method.rb	94.20% <ø> (ø)

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more