fix: use .read() instead of .content.read() in aiohttp transport

[google-labs-jules]

Fixes issue where response content is empty when using aiohttp-client-cache by using response.read() instead of response.content.read().

Rationale:
In aiohttp, .read() is the standard, high-level method for reading the full response body. It correctly handles internal state (like caching the body for subsequent calls), which is essential for compatibility with wrappers like aiohttp-client-cache. Accessing .content.read() directly bypasses this logic, leading to empty responses when the stream has already been consumed or intercepted by the caching layer.

Benefits:

• Robustness: Ensures correct behavior when google-auth is used in conjunction with aiohttp wrappers or middleware.
• Standards: Aligns with aiohttp best practices for consuming response bodies.

Risk Mitigation:

• Behavior: _CombinedResponse is designed to load the full response into memory. Changing to .read() preserves this behavior exactly; it just uses a safer accessor.
• Performance: Since aiohttp's .read() returns a reference to the bytes, there is no additional memory overhead compared to the previous implementation.
• Internal: This change is internal to the transport adapter and does not alter the public API or behavior for users not using caching libraries.

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PR created automatically by Jules for task 3355868403646689815 started by @chalmerlowe

[google-labs-jules]

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[chalmerlowe]

LGTM

[daniel-sanche]

LGTM

[chalmerlowe]

Temporarily removing the requirement for system-3.10 to pass due to a known issue with that CI/CD check that is being addressed in an separate PR #1901

[google-labs-jules]

Temporarily removing the requirement for system-3.10 to pass due to a known issue with that CI/CD check that is being addressed in an separate PR #1901

Acknowledged.