ci: migrate crash tracking tests to the test agent (#13908)

The way the current crash tracking tests are set up it does not support
any requests other than a single crash report (telemetry log). With the
new native writer, we might making `/info` requests on startup.

The current implementation of the dummy receiver is that it only ever
allows 1 single connection, but we may be making more than 1 connection
to the agent from different writers (native + crashtracker, for
example).

This change migrates the crash tracker tests to use the test agent,
reporting data to the test agent and then fetching the requests to
assert on.


Majority of the test changes are intention changes moving everything to:

```python
with utils.with_test_agent() as client:
    ...  # original test code

    report = utils.get_crash_report(client)
    assert b"string_at" in report["body"]
```

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [ ] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: brettlangdon

riotfile.py

@@ -477,7 +477,6 @@ def select_pys(min_version: str = MIN_PYTHON_VERSION, max_version: str = MAX_PYT
         Venv(
             name="internal",
             env={
-                "DD_TRACE_AGENT_URL": "http://ddagent:8126",
                 "DD_INSTRUMENTATION_TELEMETRY_ENABLED": "0",
             },
             command="pytest -v {cmdargs} tests/internal/",