chore(deps): update grpcio-health-checking requirement from <1.81,>=1.60 to >=1.60,<1.82

[dependabot]

Updates the requirements on grpcio-health-checking to permit the latest version.

[jjviscomi]

Holding this for now rather than declining it. The <1.81 cap on grpcio-health-checking is deliberate, and the precondition for lifting it (documented in the pyproject.toml comment next to the pin) is not yet met.

Why:

• grpc_api/server.py imports grpc_health.v1 at startup, so a grpcio-health-checking newer than the installed grpcio raises RuntimeError and the emulator will not start.
• Five Python example CI jobs install bqemulator editable (pip install -e ".[dev,all]") and then their hash-pinned requirements.txt. Four of them (pytest-integration, dbt-local, airflow-dag-test, pyspark-bigquery) pin grpcio==1.80.0; only export-to-gcs is on grpcio==1.81.0.
• Lifting the cap to <1.82 lets the editable install pull grpcio-health-checking==1.81, then requirements.txt pins grpcio==1.80.0 back down while leaving grpcio-health-checking at 1.81 (it is not in the lock). That is grpcio-health-checking 1.81 newer than grpcio 1.80, the exact skew the cap prevents, and it would fail those four example make test jobs.
• This PR only touches pyproject.toml, which is not in examples.yml's path filter, so those example jobs do not run here. The breakage would be latent (surfacing on the next docs/examples/** PR or the nightly sweep) rather than caught at merge.

There is no CVE forcing this bump, so we will hold until the remaining example grpcio client locks move to >=1.81 (the comment's stated precondition), then lift grpcio-health-checking and grpcio-tools together and update the comment. Leaving this open so it can be picked up at that point.