fix(test): exclude CBF and Bitcoind REST from random chain source

CBF requires dedicated peer setup and cannot work in randomized tests.
Bitcoind REST is excluded to match upstream's random range (0..3),
which only covers Esplora, Electrum, and Bitcoind RPC. Both backends
have dedicated test paths with explicit chain source selection.

Author: febyeji

tests/common/mod.rs

@@ -268,7 +268,7 @@ pub(crate) fn random_chain_source<'a>(
 		Some("bitcoind-rpc") => 2,
 		Some("bitcoind-rest") => 3,
 		Some("cbf") => 4,
-		_ => rand::random_range(0..4),
+		_ => rand::random_range(0..3),
 	};
 	match r {
 		0 => {