fix(engine): pass process.env.CI to workers

- Fixes usages of environment variables is `eslint-remote-tester.config.js`
- Fixes cache failures of ci-runner

lib/engine/engine.ts

@@ -26,8 +26,15 @@ function scanRepository(
                 repository,
                 configurationLocation: resolveConfigurationLocation(),
             },
-            // Prevent git from prompting password. Instead just fail repository cloning.
-            env: { GIT_TERMINAL_PROMPT: '0' },
+
+            // TODO: use worker.SHARE_ENV. Figure out how to combine it with GIT_TERMINAL_PROMPT
+            env: {
+                // Prevent git from prompting password. Instead just fail repository cloning.
+                GIT_TERMINAL_PROMPT: '0',
+
+                // Pass CI flag to worker_threads
+                CI: process.env.CI,
+            },
         });
 
         worker.on('message', (message: WorkerMessage) => {