build(docs): Bump starlight theme to 0.8.0 (#1287)

Bump the docs site to `@sentry/starlight-theme` 0.8.0 and refresh its
pnpm lockfile.

The docs build is currently blocked by a pre-existing invalid Starlight
sidebar slug (`configuration`); the same failure reproduces with 0.7.0.

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Requested by **David Cramer** via Junior.
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Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>

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docs/package.json

@@ -10,7 +10,7 @@
   "dependencies": {
     "@astrojs/starlight": "^0.39.2",
     "@sentry/astro": "^10.38.0",
-    "@sentry/starlight-theme": "^0.7.0",
+    "@sentry/starlight-theme": "^0.8.0",
     "astro": "^6.4.6",
     "sharp": "^0.33.5",
     "shiki": "^3.21.0"