build: use Go 1.24.2 specifically

https://github.com/golang/go/issues/73617

.github/workflows/build-syncthing.yaml

@@ -10,7 +10,7 @@ env:
   # The go version to use for builds. We set check-latest to true when
   # installing, so we get the latest patch version that matches the
   # expression.
-  GO_VERSION: "~1.24.0"
+  GO_VERSION: "1.24.2"
 
   # Optimize compatibility on the slow archictures.
   GOMIPS: softfloat