Fix broken anchor link withActiveSpan (#11129)

anchor link was broken

Author: cstavitsky

docs/platforms/javascript/common/tracing/instrumentation/custom-instrumentation/index.mdx

@@ -30,7 +30,7 @@ In contrast, **inactive spans** will never have children automatically associate
 
 A key constraint for active spans is that they can only be made active inside of a callback. This constraint exists because otherwise it becomes impossible to associate spans with the correct parent span when working with asynchronous code.
 
-In places where you are not able to wrap executing code in a callback (e.g. when working with hooks or similar) you have to work with inactive spans, and can combine this with [withActiveSpan](#with-active-span) to manually associate child spans with the correct parent span.
+In places where you are not able to wrap executing code in a callback (e.g. when working with hooks or similar) you have to work with inactive spans, and can combine this with [withActiveSpan](#withactivespan) to manually associate child spans with the correct parent span.
 
 <PlatformCategorySection supported={['browser']}>