Blur videos on AV1 codec when switching from L1T3 to L3T3 in the fly

[曾杰（der rauber）]

When switching the scalability mode from L1T3 to L3T3, the receiver side observes a very shortly video blur and recovered quickly. Test with chrome 113.0.5672.126 (arm64)  on m1 mac.

Can be reproduced by https://cnderrauber.github.io/webrtc-samples/src/content/peerconnection/pc1/ which is forked from webrtc-samples :

1. open the link and click `start`, `call`, it will establish a p2p session with av1 L1T3 scalability mode

2. click the `L3T3` button, the publisher pc will change scalability mode of encoding to L3T3, and the receiver side will observe the video becomes blur and recovered quickly.