docs: fix backend path

Signed-off-by: satotake <doublequotation@gmail.com>

docs/use-cases/1012-ci.md

@@ -147,7 +147,7 @@ backend: {
     // We use `os.#Dir` to grab a sub-directory of `source`
     code: os.#Dir & {
         from: source
-        path: "."
+        path: "./backend"
     }
 
     test: os.#Container & {