Bump astro test fixture to ^7.1.0 to clear dependabot XSS alerts

The astro-vite7 live-e2e fixture pinned astro ^6.0.0, which resolves
into the vulnerable range of three dependabot advisories:
GHSA-4g3v-8h47-v7g6 (reflected XSS via View Transition animation
properties, medium), GHSA-f48w-9m4c-m7f5 (XSS via spread attribute
names in renderHTMLElement, medium), and GHSA-7pw4-f3q4-r2p2 (XSS via
transition:* directive values, low). All three are patched by 7.1.0.

Dev-only test fixture; the vulnerable code paths (View Transitions,
transition directives, spread attributes) are not exercised by this
static, non-hydrated page, so real exposure is nil. Bumped anyway as
the cheap, correct fix. Also corrected the now-stale fixture label to
"Astro 7 + Vite 7".

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/framework-fixtures/astro-vite7/files/package.json

@@ -9,6 +9,6 @@
     "preview": "astro preview"
   },
   "devDependencies": {
-    "astro": "^6.0.0"
+    "astro": "^7.1.0"
   }
 }

tests/framework-fixtures/astro-vite7/fixture.json

@@ -1,5 +1,5 @@
 {
-  "name": "Astro 6 + Vite 7",
+  "name": "Astro 7 + Vite 7",
   "config": {
     "files": ["src/layouts/Layout.astro"],
     "insertBefore": "</body>",