Add no-var ESLint disable for TypeScript declare global blocks

CI detects no-var violations in declare global blocks, while local ESLint
does not. This appears to be an environment difference in how TypeScript
ESLint processes ambient declarations.

Adding the disable directive to match CI requirements. The declare global
syntax requires var (not let/const) per TypeScript spec.

Author: justin808

packages/react-on-rails/src/context.ts

@@ -1,10 +1,10 @@
 import type { ReactOnRailsInternal, RailsContext } from './types/index.ts';
 
 declare global {
-  /* eslint-disable vars-on-top,no-underscore-dangle */
+  /* eslint-disable vars-on-top,no-var,no-underscore-dangle */
   var ReactOnRails: ReactOnRailsInternal | undefined;
   var __REACT_ON_RAILS_EVENT_HANDLERS_RAN_ONCE__: boolean;
-  /* eslint-enable vars-on-top,no-underscore-dangle */
+  /* eslint-enable vars-on-top,no-var,no-underscore-dangle */
 }
 
 let currentRailsContext: RailsContext | null = null;