encoding/json/jsontext: fix spelling error

Change-Id: Ic1f385afbe35addba8b3c439ccb64c56b1d300c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/681795
Reviewed-by: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: kevinburke

src/encoding/json/jsontext/doc.go

@@ -10,7 +10,7 @@
 // primitive data types such as booleans, strings, and numbers,
 // in addition to structured data types such as objects and arrays.
 //
-// This package (encoding/json/jsontxt) is experimental,
+// This package (encoding/json/jsontext) is experimental,
 // and not subject to the Go 1 compatibility promise.
 // It only exists when building with the GOEXPERIMENT=jsonv2 environment variable set.
 // Most users should use [encoding/json].