chore(ci): pin mysql-connector-python to 8.0.31 for Python 3.6 [backport #4924 to 1.7] (#4956)

## Description
MySQL connector python introduced in version 8.0.32 a `__future__`
import making it incompatible with Python < 3.7

## Checklist
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when writing a release note.
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and/or [Datadog's documentation
site](https://github.com/DataDog/documentation/) is updated. Link to doc
PR in description.

## Reviewer Checklist
- [ ] Title is accurate.
- [ ] Description motivates each change.
- [ ] No unnecessary changes were introduced in this PR.
- [ ] Avoid breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [ ] Tests provided or description of manual testing performed is
included in the code or PR.
- [ ] Release note has been added and follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/contributing.html#Release-Note-Guidelines),
or else `changelog/no-changelog` label added.
- [ ] All relevant GitHub issues are correctly linked.
- [ ] Backports are identified and tagged with Mergifyio.

## Description
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## Checklist
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## Reviewer Checklist
- [ ] Title is accurate.
- [ ] Description motivates each change.
- [ ] No unnecessary changes were introduced in this PR.
- [ ] Avoid breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [ ] Tests provided or description of manual testing performed is
included in the code or PR.
- [ ] Release note has been added and follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/contributing.html#Release-Note-Guidelines),
or else `changelog/no-changelog` label added.
- [ ] All relevant GitHub issues are correctly linked.
- [ ] Change contains telemetry where appropriate (logs, metrics, etc.).
- [ ] Telemetry is meaningful, actionable and does not have the
potential to leak sensitive data.

Co-authored-by: Federico Mon <[email protected]>

Author: Yun-Kim

riotfile.py

@@ -1172,7 +1172,11 @@ def select_pys(min_version=MIN_PYTHON_VERSION, max_version=MAX_PYTHON_VERSION):
                     pkgs={"mysql-connector-python": ["==8.0.5", "<8.0.24"]},
                 ),
                 Venv(
-                    pys=select_pys(min_version="3.6", max_version="3.9"),
+                    pys=["3.6"],
+                    pkgs={"mysql-connector-python": ["==8.0.5", "==8.0.31"]},
+                ),
+                Venv(
+                    pys=select_pys(min_version="3.7", max_version="3.9"),
                     pkgs={"mysql-connector-python": ["==8.0.5", ">=8.0", latest]},
                 ),
                 Venv(