update rust nightly version to 2026-04-17

This matches rust-bitcoin.

Author: apoelstra

Cargo.toml

@@ -10,7 +10,7 @@ documentation = "https://docs.rs/elements/"
 edition = "2018"
 
 [workspace.metadata.rbmt.toolchains]
-nightly = "nightly-2025-09-27"
+nightly = "nightly-2026-04-17"
 stable = "1.95.0"
 
 [features]