feat: Add a skip_token_revoke input for configuring token revocation (#54)

Fixes https://github.com/actions/create-github-app-token/issues/55

Currently, `actions/create-github-app-token` always/unconditionally
revokes the installation access token in a `post` step, at the
completion of the current job. This prevents tokens from being used in
other jobs.

This PR makes this behavior configurable:
- When the `skip-token-revoke` input is not specified (i.e. by default),
the token is revoked in a `post` step (i.e. the current behavior).
- When the `skip-token-revoke` input is set to a truthy value (e.g.
`"true"`[^1]), the token is not revoked in a `post` step.

This PR adds a test for the `skip-token-revoke: "true"` case.

This is configurable in other app token actions, e.g.
[tibdex/github-app-token](3eb77c7243/README.md (L46-L47))
and
[wow-actions/use-app-token](cd772994fc/README.md (L132)).

[^1]: Note that `"false"` is also truthy: `Boolean("false")` is `true`.
If we think that’ll potentially confuse folks, I can require
`skip-token-revoke` to be set explicitly to `"true"`.

dist/post.cjs

@@ -2973,6 +2973,11 @@ var import_core = __toESM(require_core(), 1);
 
 // lib/post.js
 async function post(core2, request2) {
+  const skipTokenRevoke = Boolean(core2.getInput("skip_token_revoke"));
+  if (skipTokenRevoke) {
+    core2.info("Token revocation was skipped");
+    return;
+  }
   const token = core2.getState("token");
   if (!token) {
     core2.info("Token is not set");