test(google_adk): allow pre-release opentelemetry-resourcedetector-gcp to fix dependency resolution

[mikeldking]

fix google_adk canary: dependency resolution failure

Root cause

The canary cron's py310-ci-google_adk-latest and py314-ci-google_adk-latest
environments failed at the uv pip install -r test-requirements.txt step (before
any tests ran) with an unsatisfiable resolution:

Because only opentelemetry-resourcedetector-gcp<1.5.0.dev0 is available and
opentelemetry-exporter-gcp-trace>=1.9.0 depends on
opentelemetry-resourcedetector-gcp>=1.5.0.dev0, we can conclude that
opentelemetry-exporter-gcp-trace>=1.9.0 cannot be used.
And because google-adk==1.2.1 depends on opentelemetry-exporter-gcp-trace>=1.9.0
and you require google-adk==1.2.1, your requirements are unsatisfiable.

This is an upstream packaging change, not a code regression:

• google-adk (via opentelemetry-exporter-gcp-trace) now pulls in
  opentelemetry-exporter-gcp-trace>=1.9.0.
• The newer opentelemetry-exporter-gcp-trace releases require
  opentelemetry-resourcedetector-gcp>=1.5.0.dev0, which is only published as a
  pre-release (e.g. 1.12.0a0); no matching stable release exists.
• uv does not enable pre-releases for a package unless it is requested with a
  pre-release marker in a direct requirement. Because the marker only appears
  transitively, uv refused to select the pre-release and resolution failed. The
  uv hint in the log spells this out.

Fix

Add opentelemetry-resourcedetector-gcp>=1.5.0.dev0 as a direct entry in the
package's test-requirements.txt. The explicit pre-release marker tells uv it may
select the pre-release for that package, allowing the google-adk dependency tree
(opentelemetry-exporter-gcp-trace 1.12.0 / opentelemetry-resourcedetector-gcp 1.12.0a0) to resolve. This is a test-only change; the instrumentor's runtime
dependencies are unchanged.

Validation

Ran from the repository root:

uvx --with tox-uv tox -c python/tox.ini r -e py310-ci-google_adk-latest -- -ra -x
uvx --with tox-uv tox -c python/tox.ini r -e py314-ci-google_adk-latest -- -ra -x

Both environments now resolve dependencies, upgrade to google-adk==2.5.0 (latest),
and pass: 24 passed each, with ruff format, ruff check, and mypy all clean.

[github-actions]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.