fix: skip integration tests when E2B_API_KEY secret is not set

Gate the "Run integration tests" CI step on the E2B_API_KEY env var
being present, matching the pattern used by other integrations (e.g.
cohere). Without this the step exits with code 5 (no tests collected)
because there are no integration-marked tests and no API key is
configured yet.

Also exposes E2B_API_KEY from secrets at the workflow env level so
it will be available once a maintainer adds the secret to the repo.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: tholor

.github/workflows/e2b.yml

@@ -29,6 +29,7 @@ concurrency:
 env:
   PYTHONUNBUFFERED: "1"
   FORCE_COLOR: "1"
+  E2B_API_KEY: ${{ secrets.E2B_API_KEY }}
   TEST_MATRIX_OS: '["ubuntu-latest", "windows-latest", "macos-latest"]'
   TEST_MATRIX_PYTHON: '["3.10", "3.14"]'
 
@@ -102,6 +103,7 @@ jobs:
           path: python-coverage-comment-action-e2b.txt
 
       - name: Run integration tests
+        if: env.E2B_API_KEY != ''
         run: hatch run test:integration-cov-append-retry
 
       - name: Store combined coverage