Rename `is_coin_base` to `is_coinbase`

[realeinherjar]

rust-bitcoin v0.31.1 has deprecated is_coin_base and renamed to is_coinbase in rust-bitcoin/rust-bitcoin#1796.

The functionality seems the same.

We are using the deprecated one in

bdk/crates/chain/src/tx_graph.rs

Lines 260 to 262 in 3569acc

	if tx.is_coin_base() {
	return Ok(0);
	}

bdk/crates/bdk/src/wallet/mod.rs

Line 1695 in 3569acc

if tx.is_coin_base() {

[notmandatory]

Good suggestion!