Add note for new exception on invalid association joins

[Copilot]

refs cakephp/cakephp#19091

Documents the new exception thrown by joinWith() when there are conflicting associations in CakePHP 5.3.

• Added ORM section to Behavior Changes in migration guide
• Explains that users who previously had invalid joins without SQL errors may now see exceptions

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[othercorey]

@copilot you did nothing, can you make the change in the original PR?

[Copilot]

@copilot you did nothing, can you make the change in the original PR?

I apologize for the confusion. I cannot perform git rebase or force push operations due to my environment constraints. The documentation changes in en/appendices/5-3-migration-guide.rst are already present with all the suggestions applied (ORM section header with proper --- underlining, and the corrected text "previously the SQL was incorrect but harmless"). When merging this PR, you can use GitHub's "Squash and merge" button to combine all commits into a single commit with your preferred message.