go.mod: format require section

Change-Id: Ia54ecb1cd5f05c2502acd13f1cf3db5f66070d15
Reviewed-on: https://go-review.googlesource.com/c/arch/+/668335
Reviewed-by: Carlos Amedee <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Junyang Shao <[email protected]>
Reviewed-by: Sean Liao <[email protected]>

Author: zchee

go.mod

@@ -2,6 +2,7 @@ module golang.org/x/arch
 
 go 1.23.0
 
-require rsc.io/pdf v0.1.1
-
-require gopkg.in/yaml.v3 v3.0.1
+require (
+	gopkg.in/yaml.v3 v3.0.1
+	rsc.io/pdf v0.1.1
+)