fix(grpc): add isolation_scope to async server interceptor

[robinvd]

Description

Fixes #5894

The async gRPC server interceptor was missing isolation_scope() wrapping, causing scope state to leak between concurrent requests. The sync interceptor already had this. This PR adds the missing isolation scope to the async unary_unary handler and adds a test proving request isolation.

Issues

• resolves: gRPC aio ServerInterceptor missing isolation_scope per request #5894

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

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New Features ✨

• (integrations) Instrument pyreqwest tracing by servusdei2018 in #5682

Bug Fixes 🐛

• (grpc) Add isolation_scope to async server interceptor by robinvd in #5940

Internal Changes 🔧

• (opentelemetry) Ignore mypy error by alexander-alderman-webb in #5927
• Fix license metadata in setup.py by sl0thentr0py in #5934
• Update validate-pr workflow by stephanie-anderson in #5931

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