fix(e2e): Pin astro version in astro-6 test app

Astro 6.3.0 removed `getAdapterLogger()` from `BaseApp`, breaking
compatibility with `@astrojs/node@10.0.6` which still calls it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: nicohrubec

dev-packages/e2e-tests/test-applications/astro-6/package.json

@@ -16,7 +16,7 @@
     "@playwright/test": "~1.56.0",
     "@sentry-internal/test-utils": "link:../../../test-utils",
     "@sentry/astro": "file:../../packed/sentry-astro-packed.tgz",
-    "astro": "^6.0.6"
+    "astro": "6.0.6"
   },
   "volta": {
     "node": "22.22.0",