Use onlyGovernance to restrict upgrades for Governor with UUPS

[elisafalk]

This pull request addresses issue #144 by modifying the Governor contract to utilize the onlyGovernance modifier for the _authorizeUpgrade function when the contract is set as UUPS upgradeable.

Changes Made:

• Updated the setUpgradeableGovernor function in set-upgradeable.ts to replace the onlyOwner modifier with onlyGovernance for the _authorizeUpgrade function.
• Ensured that the UUPS upgradeability is correctly implemented in the Governor contract, allowing for governance-based upgrades.

Fixes #144

[elisafalk]

@ericglau I was having some conflict in the previous PR so I had to close it. Here is a new PR where the master branch is up to date. Please review and let me know if I need to change anything.

[ericglau]

• I've added a comment where a refactor would be useful.
• Please add a changeset according to steps in https://github.com/OpenZeppelin/contracts-wizard/blob/master/CONTRIBUTING.md#adding-changesets

[elisafalk]

@ericglau Could you kindly check if everything is alright now?

[ericglau]

Thanks for the updates. I pushed some refactors and fixed the tests. We'll do some additional reviews before merging.

[elisafalk]

@ericglau @CoveMB thanks for the feedback. Please merge this PR if it looks correct.

[CoveMB]

Thanks for contributing

[elisafalk]

@ericglau @CoveMB Hope you are having a good day. Thank you so much for your guidance in resolving this issue — it’s been a great learning experience and has definitely boosted my confidence to take on more issues. If everything looks good, could you kindly proceed with the merge?
Thanks again!