[BUG]: RawValue no longer supports mysql functions

[ALameLlama]

Hello!

• Type: bug fix
• Link to issue: [BUG]: RawValue no longer supports mysql functions #16037

In raising this pull request, I confirm the following:

• I have read and understood the Contributing Guidelines
• I have checked that another pull request for this purpose does not exist
• I wrote some tests for this PR
• I have updated the relevant CHANGELOG
• I have created a PR for the documentation about this change

Small description of change:
I've updated the changed check on the Model.zep to have a separate comparison variable instead of overwriting the value, overwriting the value with the value->getValue() is turning it into a string and causing issues deeper in the update at phalcon\Db\Adapter\AbstractAdapter.zep:1198-1202

Instead of the placeholders[] being something like:
'`last_updated` = now()'

It's passing:
'`last_updated` = ?' and then passing 'now()' in the bind parameters

Thanks

[niden]

Thank you @LlamaDuckGoose !!