insomnia: update livecheck

Casks/i/insomnia.rb

@@ -8,8 +8,12 @@ cask "insomnia" do
   desc "HTTP and GraphQL Client"
   homepage "https://insomnia.rest/"
 
+  # Upstream previously used a date-based version scheme (e.g., `2023.5.8`)
+  # before switching to a typical `8.1.0` format. The date-based versions are
+  # numerically higher, so we have to avoid matching them.
   livecheck do
-    regex(/core@v?(\d{1,3}(?:\.\d+)+)(?!.)/i)
+    url :url
+    regex(/^core@v?(\d{1,3}(?:\.\d+)+)$/i)
   end
 
   auto_updates true