Fix grammar errors in docs

[mintlify]

Summary

• Fixed "emits a auto event" → "emits an auto event" in integrations/middleware-auto-error.mdx (incorrect article before vowel sound)
• Fixed "Note: that global lock is scoped" → "Note that the global lock is scoped" in concurrency/events-global-serial.mdx (misplaced colon and missing article)

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Summary by cubic

Fix grammar in docs for clarity. Updated docs/integrations/middleware-auto-error.mdx to say "emits an auto event" and docs/concurrency/events-global-serial.mdx to "Note that the global lock is scoped".

^{Written for commit 01bff67. Summary will update on new commits.}