renovate: Update dependency go to v1.25.6 (#38)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

go.mod

@@ -2,7 +2,7 @@ module github.com/luno/bchutil
 
 go 1.25
 
-toolchain go1.25.5
+toolchain go1.25.6
 
 require (
 	github.com/btcsuite/btcd v0.25.0