_content/doc/go1.24: add issue link to synctest relnotes

For golang/go#67434

Change-Id: I6d6f0eb4d498ec65e05bedb40b68b778f7ad591f
Reviewed-on: https://go-review.googlesource.com/c/website/+/635375
Reviewed-by: Michael Pratt <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Damien Neil <[email protected]>

Author: neild

_content/doc/go1.24.md

@@ -260,6 +260,8 @@ See the package documentation for more details.
 The `synctest` package is experimental and must be enabled by
 setting `GOEXPERIMENT=synctest` at build time.
 The package API is subject to change in future releases.
+See [issue #67434](/issue/67434) for more information and
+to provide feeback.
 
 ### Minor changes to the library {#minor_library_changes}