fix(deps): update go toolchain directive to v1.27.2

Fixes stdlib advisories GO-2026-6603, 6605, 6607, 6608, 6610, 6611, 6613 and 6617 (same change as Renovate PR #427).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01C8SW6vsbkrTKjLNatQ8JTg

go.mod

@@ -2,7 +2,7 @@ module gitlab.com/unboundsoftware/cron-checker
 
 go 1.26.0
 
-toolchain go1.27.1
+toolchain go1.27.2
 
 require (
 	github.com/alecthomas/kingpin/v2 v2.4.0