55# cbBTC and tBTC markets: rate to 2 x 1.32% and AMM fee to 1.82% (after Curve vote 1491)

Set the yb-cbBTC (market 8) and yb-tBTC (market 9) borrow/refuel rate to 2 * 1.32% per year on crvUSD and their AMM fee to 1.82%, matching what was already done for yb-WBTC. Both changes belong together with the new crvUSD/cbBTC and crvUSD/tBTC pool parameters and fee policies installed by Curve ownership vote 1491, so this proposal is guarded: it first asserts that both pools already have a policy contract set (POLICY() != 0x0) and reverts otherwise. It therefore cannot take effect before the Curve vote is executed, and can simply be executed once that has happened.