feat(outputs): app-slug and installation-id (#105)

It is convenient to use `https://api.github.com/users/$app_slug[bot]` to
obtain the corresponding account ID later.
Then build `Signed-off-by: $app_slug[bot]
<$id+$app_slug[bot]@users.noreply.github.com>`.

Currently, there is no Linux environment to build test snapshot files

tests/main.js

@@ -54,8 +54,9 @@ export async function test(cb = (_mockPool) => {}, env = DEFAULT_ENV) {
 
   // Calling `auth({ type: "app" })` to obtain a JWT doesn’t make network requests, so no need to intercept.
 
-  // Mock installation id request
+  // Mock installation ID and app slug request
   const mockInstallationId = "123456";
+  const mockAppSlug = "github-actions";
   const owner = env.INPUT_OWNER ?? env.GITHUB_REPOSITORY_OWNER;
   const repo = encodeURIComponent(
     (env.INPUT_REPOSITORIES ?? env.GITHUB_REPOSITORY).split(",")[0]
@@ -72,7 +73,7 @@ export async function test(cb = (_mockPool) => {}, env = DEFAULT_ENV) {
     })
     .reply(
       200,
-      { id: mockInstallationId },
+      { id: mockInstallationId, "app_slug": mockAppSlug },
       { headers: { "content-type": "application/json" } }
     );