v2.3: svm: use load_transaction_account for initial nonce load (backport of #6869)

[mergify]

Problem

we use load_account() to load the nonce account for validation, but this is potentially confusing because it occurs prior to full transaction loading

Summary of Changes

use load_transaction_account() instead

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This is an automatic backport of pull request #6869 done by Mergify.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.8%. Comparing base (ba9371d) to head (67f8ee2).

Additional details and impacted files

@@           Coverage Diff           @@
##             v2.3    #6874   +/-   ##
=======================================
  Coverage    82.8%    82.8%           
=======================================
  Files         850      850           
  Lines      379746   379746           
=======================================
+ Hits       314738   314748   +10     
+ Misses      65008    64998   -10     

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