OpenZeppelin Contracts's governor proposal creation may be blocked by frontrunning
### Impact
By frontrunning the creation of a proposal, an attacker can become the proposer and gain the ability to cancel it. The attacker can do this repeatedly to try to prevent a proposal from being proposed at all.
This impacts the `Governor` contract in v4.9.0 only, and the `GovernorCompatibilityBravo` contract since v4.3.0.
### Patches
The problem has been patched in 4.9.1 by introducing opt-in frontrunning protection.
### Workarounds
Submit the proposal creation transaction to an endpoint with frontrunning protection.
### Credit
Reported by Lior Abadi and Joaquin Pereyra from Coinspect.
### References
https://www.coinspect.com/openzeppelin-governor-dos/