install langchain_community to fix failed executor e2e test case

[lalala123123]

Description

https://github.com/microsoft/promptflow/actions/runs/9346975864/job/25723044774
Miss required package in executor test ci

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

All Promptflow Contribution checklist:

• The pull request does not introduce [breaking changes].
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.
• Create an issue and link to the pull request to get dedicated review from promptflow team. Learn more: suggested workflow.

General Guidelines and Best Practices

• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[github-actions]

Test Results

    24 files      24 suites   2h 25m 15s ⏱️
 1 052 tests  1 044 ✅   5 💤 3 ❌
12 504 runs  12 389 ✅ 108 💤 7 ❌

For more details on these failures, see this check.

Results for commit 1cd1fc6.