@envelop/sentry fails subscriptions

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used [patch-package](https://github.com/ds300/patch-package) to patch `@envelop/sentry@3.5.0` for the project I'm working on.

`Symbol('sentryTracing')` is undefined when using subscriptions with graphql-ws (together with fastify and yoga) and as such causes the subscription call itself to fail. Not sure if the package is meant to be used with subscriptions - but at least it shouldn't crash :)

Here is the diff that solved my problem:

```diff
diff --git a/node_modules/@envelop/sentry/cjs/index.js b/node_modules/@envelop/sentry/cjs/index.js
index 1cd1c34..24ffd45 100644
--- a/node_modules/@envelop/sentry/cjs/index.js
+++ b/node_modules/@envelop/sentry/cjs/index.js
@@ -36,6 +36,10 @@ const useSentry = (options = {}) => {
}
const onResolverCalled = trackResolvers
? ({ args: resolversArgs, info, context }) => {
+ if(!context[sentryTracingSymbol]){
+ console.warn('no sentryTracingSymbol present, skipping tracing')
+ return null
+ }
const { rootSpan, opName, operationType } = context[sentryTracingSymbol];
if (rootSpan) {
const { fieldName, returnType, parentType } = info;
```

This issue body was [partially generated by patch-package](https://github.com/ds300/patch-package/issues/296).

Start with @envelop/sentry/cjs/index.js and useSentry’s onResolverCalled path while reproducing a subscription through graphql-ws. Done means subscriptions no longer fail when sentryTracing is absent, while existing resolver tracing behavior remains intact.

Written by the indexing model from the issue text.