component/golang/1.21: bugfix version up 9 -> 13

As suggested by Kirill, this patch updates the bugfix release version of
golang 1.21. None of the other older golang version have any new bugfix
release since 620e2a18.

/review-by @kirr
/reviewed-on !1646

component/golang/buildout.cfg

@@ -145,8 +145,8 @@ environment-extra =
 
 [golang1.21]
 <= golang-common
-url = https://go.dev/dl/go1.21.9.src.tar.gz
-md5sum = 3cc8b75a5499b5d309f267e21c3432df
+url = https://go.dev/dl/go1.21.13.src.tar.gz
+md5sum = 3454362fc56df5020920e43fee2776ab
 # go1.21 requires go1.17.13 to bootstrap (see https://go.dev/blog/rebuild)
 environment-extra =
   GOROOT_BOOTSTRAP=${golang1.17:location}