go.mod: adopt the require layout Go 1.27 tidy produces

Go 1.27 collapses requires into one direct and one indirect block, so the
modernc lockstep note has to live inside a block to survive tidy.
-compat=1.27 is a no-op now that the go directive is 1.27.

flakehashes.json

@@ -1,6 +1,6 @@
 {
   "vendor": {
-    "goModSum": "sha256-9hyJR6xdvbNGw2JHqfObB6V3LJUTPDEfppsFE7Eje2U=",
-    "sri": "sha256-4ZaF8fAArd7tvJeHvo02c4MRWrDRcEUxzi2Y0h8AFVc="
+    "goModSum": "sha256-c5zqlgQKbVs9Y9FXHkdZh17FqyXPLh/j+XYQj/IPW8k=",
+    "sri": "sha256-zWcaRben+px9w6NcUPkYfR6DbBJhwdYsXcZ5cm95hmo="
   }
 }