Fix credential cleanup when env exports are disabled

[1seal]

summary

this decouples post-step credentials cleanup from export_environment_variables.

when create_credentials_file=true and cleanup_credentials=true, the action now saves the created credentials path with saveState in the main step and reads it with getState in the post step. this keeps cleanup working even when export_environment_variables=false.

changes

• save the created credentials path in src/main.ts
• read saved state first in src/post.ts, with env var fallback
• add a regression test covering the no-env-export cleanup path
• rebuild dist/main and dist/post

testing

• npm test
• npm run build