[next] replace next export with output: export in tests (#10756)

`next export` has been deprecated on the latest Next.js canary so these
tests will no longer pass.

This changes it to use `output: export` from `next.config.js` instead.

---------

Co-authored-by: JJ Kasper <jj@jjsweb.site>

.changeset/modern-walls-refuse.md

@@ -0,0 +1,2 @@
+---
+---

packages/next/test/fixtures/00-trailing-slash-add-export/next.config.js

@@ -1,4 +1,5 @@
 module.exports = {
+  output: 'export',
   generateBuildId() {
     return 'testing-build-id';
   },

packages/next/test/fixtures/00-trailing-slash-add-export/package.json

@@ -1,6 +1,6 @@
 {
   "scripts": {
-    "build": "next build && next export"
+    "build": "next build"
   },
   "dependencies": {
     "next": "canary",

packages/next/test/fixtures/10-export-cache-headers/next.config.js

@@ -1,4 +1,5 @@
 module.exports = {
+  output: 'export',
   generateBuildId() {
     return 'testing-build-id';
   },

packages/next/test/fixtures/10-export-cache-headers/package.json

@@ -1,6 +1,6 @@
 {
   "scripts": {
-    "now-build": "next build && next export"
+    "now-build": "next build"
   },
   "dependencies": {
     "next": "canary",

packages/next/test/fixtures/11-export-clean-urls/next.config.js

@@ -1,4 +1,5 @@
 module.exports = {
+  output: 'export',
   generateBuildId() {
     return 'testing-build-id';
   },

packages/next/test/fixtures/11-export-clean-urls/package.json

@@ -1,6 +1,6 @@
 {
   "scripts": {
-    "vercel-build": "next build && next export"
+    "vercel-build": "next build"
   },
   "dependencies": {
     "next": "canary",

packages/next/test/fixtures/13-export-custom-routes/next.config.js

@@ -1,4 +1,5 @@
 module.exports = {
+  output: 'export',
   generateBuildId() {
     return 'testing-build-id';
   },

packages/next/test/fixtures/13-export-custom-routes/package.json

@@ -1,6 +1,6 @@
 {
   "scripts": {
-    "build": "next build && next export"
+    "build": "next build"
   },
   "dependencies": {
     "next": "canary",