termio: don't leak VTE_VERSION into child processes

This variable is used by gnome-terminal and other VTE-based terminals.
We don't want our child processes to think we're running under VTE.

src/termio/Exec.zig

@@ -857,6 +857,8 @@ const Subprocess = struct {
         }
 
         // Don't leak these environment variables to child processes.
+        env.remove("VTE_VERSION");
+
         if (comptime build_config.app_runtime == .gtk) {
             env.remove("GDK_DEBUG");
             env.remove("GDK_DISABLE");