docs: matchMedia mock implementation to testing docs (chakra-ui#10424)

chore: matchMedia mock implementation to testing docs

Added a mock implementation for matchMedia to the testing documentation.

Author: bwcr

apps/www/content/docs/components/concepts/testing.mdx

@@ -62,6 +62,21 @@ const { window } = new JSDOM()
 vi.stubGlobal("ResizeObserver", ResizeObserver)
 window["ResizeObserver"] = ResizeObserver
 
+// matchMedia mock
+Object.defineProperty(window, "matchMedia", {
+  writable: true,
+  value: vi.fn().mockImplementation((query) => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(), // deprecated
+    removeListener: vi.fn(), // deprecated
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});
+
 // IntersectionObserver mock
 const IntersectionObserverMock = vi.fn(() => ({
   disconnect: vi.fn(),