update code snippet format in OAuth docs

[horeaporutiu]

improves on #1306. Currently the highlights look inconsistent. This change should make them consistent.
Fixes #1318

Summary

Describe the goal of this PR. Mention any related Issue numbers.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #1319 (e12fd83) into main (5e64acd) will not change coverage.
The diff coverage is n/a.

❗ Current head e12fd83 differs from pull request most recent head 3910d5e. Consider uploading reports for the commit 3910d5e to get more accurate results

@@           Coverage Diff           @@
##             main    #1319   +/-   ##
=======================================
  Coverage   72.88%   72.88%           
=======================================
  Files          17       17           
  Lines        1479     1479           
  Branches      442      442           
=======================================
  Hits         1078     1078           
  Misses        311      311           
  Partials       90       90           

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[seratch]

Indeed, it's not great:

[horeaporutiu]

Looks better now!