fixup: Symbol.for for consistency if multiple versions installed

Author: mcous

src/stubs.ts

@@ -7,7 +7,7 @@ import { NotAMockFunctionError } from './errors.ts'
 import { getFallbackImplementation } from './fallback-implementation.ts'
 import type { AnyCallable, Mock, ParametersOf } from './types.ts'
 
-const BEHAVIORS_KEY = Symbol('behaviors')
+const BEHAVIORS_KEY = Symbol.for('vitest-when:behaviors')
 
 interface WhenStubImplementation<TFunc extends AnyCallable> {
   (...args: ParametersOf<TFunc>): unknown