Update dependency go to v1.25.6

Author: renovate[bot]

go.mod

@@ -2,7 +2,7 @@ module github.com/projectsyn/steward
 
 go 1.25.0
 
-toolchain go1.25.3
+toolchain go1.25.6
 
 require (
 	github.com/alecthomas/kingpin/v2 v2.4.0