_content/blog: fix link

Change-Id: Ibba143ab2f91f76832d2c3a37f216f5cfc443ac6
Reviewed-on: https://go-review.googlesource.com/c/website/+/464021
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Eli Bendersky <eliben@google.com>

_content/blog/go1.20.md

@@ -27,7 +27,7 @@ many improvements to tooling and the library, and better overall performance.
 
 ## Language changes
 
-- The predeclared [`comparable`](ref/spec#Type_constraints) constraint is
+- The predeclared [`comparable`](/ref/spec#Type_constraints) constraint is
 now also [satisfied](/ref/spec#Satisfying_a_type_constraint) by
 ordinary [comparable types](/ref/spec#Comparison_operators), such as interfaces,
 which will simplify generic code.