Update dependency langchain_community to v0.3.21

[renovate]

This PR contains the following updates:

Package	Type	Update	Change	OpenSSF
langchain_community (changelog)	project.dependencies	patch	==0.3.19 -> ==0.3.21

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Configuration

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[renovate]

⚠️ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

♻ Renovate will retry this branch, including artifacts, only when one of the following happens:

• any of the package files in this branch needs updating, or
• the branch becomes conflicted, or
• you click the rebase/retry checkbox if found above, or
• you rename this PR's title to start with "rebase!" to trigger it manually

The artifact failure details are included below:

File name: uv.lock

Command failed: uv lock --upgrade-package langchain-community
Using CPython 3.12.4
  × No solution found when resolving dependencies for split
  │ (python_full_version >= '3.10' and python_full_version < '3.12.4'):
  ╰─▶ Because langchain-community==0.3.21 depends on
      langchain-core>=0.3.51,<1.0.0 and your project depends on
      langchain-community==0.3.21, we can conclude that your project depends
      on langchain-core>=0.3.51,<1.0.0.
      And because your project depends on langchain-core==0.3.45 and your
      project requires mucgpt[test], we can conclude that your project's
      requirements are unsatisfiable.