test(nextjs): Run nextjs-16 on Bun, Deno and Cloudflare

dev-packages/e2e-tests/README.md

@@ -136,16 +136,20 @@ Apps like `cloudflare-workers-send-to-sentry` deploy the built app as a real Wor
 
 ## Runtime variants (Bun, Deno, Cloudflare)
 
-To test a framework on a runtime other than Node.js, add an `optionalVariants` entry to the existing test app instead of
-creating a new app. `react-router-8-framework` is the reference setup.
+To test a framework on a runtime other than Node.js, add a variant to the existing test app instead of creating a new
+app: `variants` run as required CI jobs, `optionalVariants` as optional ones. `react-router-8-framework` is the
+reference setup.
 
 - **`RUNTIME` env var**: `node` (default), `bun`, `deno` or `cloudflare`. Read it with `getRuntime()` from
   `@sentry-internal/test-utils`, which throws on any other value. Tests branch on it where the runtimes are expected to
   differ (for example `platform` or `sdk.name`).
 - **SDK per runtime**: each runtime inits its own SDK, the way a user of that runtime would: Node the framework SDK
   (`instrument.mjs`), Bun `@sentry/bun` (`instrument.bun.mjs`), Deno `@sentry/deno` (`instrument.deno.mjs`) and
   Cloudflare `@sentry/cloudflare`. The framework SDK only provides the framework wrappers on the other runtimes, so
-  values that come from its `init()` (`sdk.name`, default integrations) are Node-only.
+  values that come from its `init()` (`sdk.name`, default integrations) are Node-only. Next.js is different: it loads
+  `instrumentation.ts` on every runtime, so `nextjs-16` calls `init()` of `@sentry/nextjs` on Bun and Deno too, and
+  adds the integrations of `@sentry/bun` or `@sentry/deno` that replace the Node instrumentation those runtimes do not
+  trigger.
 - **Start commands**: `playwright.config.mjs` selects the start command with `getRuntime()`. Bun and Deno use the same build
   as Node and only change the start command, for example
   `bun --bun --preload ./instrument.bun.mjs ./node_modules/@react-router/serve/bin.cjs ./build/server/index.js` and