_content/doc/go1.21: fix grammar error

Fixes golang/go#61855

Change-Id: I7affe4337395c5f6cddb07ca92eef6249806100a
Reviewed-on: https://go-review.googlesource.com/c/website/+/517217
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

_content/doc/go1.21.html

@@ -193,7 +193,7 @@ Do not send CLs removing the interior tags from such phrases.
   It also gives better error reporting for projects that make use of new Go features:
   when the problem is that a newer Go version is needed,
   that problem is reported clearly, instead of attempting to build the code
-  and instead printing errors about unresolved imports or syntax errors.
+  and printing errors about unresolved imports or syntax errors.
 </p>
 
 <p>