ci: Fix failing arq, fastapi tests on 3.7; update test matrix (#5258)

### Description
Looks like some of our test suites on Python 3.7 started failing because
they're transitively pulling in a pydantic version that uses the walrus
operator.

#### Issues
<!--
* resolves: #1234
* resolves: LIN-1234
-->

#### Reminders
- Please add tests to validate your changes, and lint your code using
`tox -e linters`.
- Add GH Issue ID _&_ Linear ID (if applicable)
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commit](https://develop.sentry.dev/engineering-practices/commit-messages/#type)
style (`feat:`, `fix:`, `ref:`, `meta:`)
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Author: sentrivana

scripts/populate_tox/config.py

@@ -34,6 +34,7 @@
         "deps": {
             "*": ["async-timeout", "pytest-asyncio", "fakeredis>=2.2.0,<2.8"],
             "<=0.23": ["pydantic<2"],
+            "py3.7": ["pydantic<1.10.25"],
         },
         "num_versions": 2,
     },
@@ -133,6 +134,7 @@
             # deprecated argument.
             "<0.110.1": ["httpx<0.28.0"],
             "py3.6": ["aiocontextvars"],
+            "py3.7": ["pydantic<1.10.25"],
         },
     },
     "flask": {