The external input weight test in wallet_fundrawtransaction.py made transactions at the minimum relay fee. However due to ECDSA sometimes making a shorter signature than expected, the size estimate (and therefore the funded fee) ends up being a little bit too low, which results in the final transaction being under the min relay fee. We can compensate for this by just using a feerate higher than the minrelayfee as the actual feerate itself does not matter in this test.
Fixes #28437