build: Use Go 1.19.6 for Windows

.github/workflows/build-syncthing.yaml

@@ -6,7 +6,7 @@ on:
 
 env:
   # The go version to use for builds.
-  GO_VERSION: "1.19.5"
+  GO_VERSION: "1.19.6"
 
   # Optimize compatibility on the slow archictures.
   GO386: softfloat