bump the browserslist version to silence a warning in CI (#86625)

e.g. https://github.com/vercel/next.js/runs/56663260329

```
● config-output-export › should work with getStaticPaths and fallback false

    expect(received).toBeEmpty()

    Expected value to be empty received:
      "[baseline-browser-mapping] The data in this module is over two months old.  To ensure accurate Baseline data, please update: `npm i baseline-browser-mapping@latest -D`
    "

```

web-platform-dx/baseline-browser-mapping#105 is discussing this

Author: lukesandberg

package.json

@@ -175,7 +175,7 @@
     "alex": "9.1.0",
     "async-sema": "3.0.1",
     "babel-plugin-react-compiler": "0.0.0-experimental-3fde738-20250918",
-    "browserslist": "4.26.2",
+    "browserslist": "4.28.0",
     "buffer": "5.6.0",
     "cheerio": "0.22.0",
     "cookie": "0.4.1",
@@ -311,7 +311,7 @@
   "pnpm": {
     "overrides": {
       "webpack": "5.98.0",
-      "browserslist": "4.26.2",
+      "browserslist": "4.28.0",
       "caniuse-lite": "1.0.30001746",
       "@types/node": "20.17.6",
       "@babel/core": "7.26.10",

packages/next/package.json

@@ -234,7 +234,7 @@
     "babel-plugin-transform-define": "2.0.0",
     "babel-plugin-transform-react-remove-prop-types": "0.4.24",
     "browserify-zlib": "0.2.0",
-    "browserslist": "4.26.2",
+    "browserslist": "4.28.0",
     "buffer": "5.6.0",
     "busboy": "1.6.0",
     "bytes": "3.1.1",