test(django): Fix flaky cache tests by using uuid for cache LOCATION (#7444)

## Root cause

`test_cache_spans_item_size[True]` and
`test_cache_spans_decorator[True]` have been intermittently failing on
master (observed 3x each in the last ~150 CI runs, e.g. [run
34096255656](https://github.com/getsentry/sentry-python/actions/runs/34096255656))
with:

```
tests/integrations/django/test_cache_module.py:764: in test_cache_spans_item_size
    assert not spans[0]["attributes"]["cache.hit"]
E   assert not True
```

`use_django_caching` / `use_django_caching_with_middlewares` gave each
test a "unique" Django `LocMemCache` namespace via
`"unique-snowflake-%s" % random.randint(1, 1_000_000)`. Django's
`LocMemCache` backend keeps its data keyed by `LOCATION` in a
module-level dict for the lifetime of the test process. With only ~1e6
possible values and hundreds of tests using this fixture in a session,
the birthday problem gives a non-trivial chance that two different test
invocations pick the *same* `LOCATION`. When that happens, a later
test's very first `cache.get()` call sees a cache entry left behind by
an earlier (unrelated) test, so `cache.hit` comes back `True` instead of
the expected `False`, failing the assertion.

## Fix

Use `uuid.uuid4()` (already imported in this file) instead of
`random.randint(1, 1_000_000)` for the cache `LOCATION`, guaranteeing no
collisions across the test session. Removed the now-unused `random`
import.

## Verification

- `pytest tests/integrations/django/test_cache_module.py` — 37 passed
- `ruff check tests/integrations/django/test_cache_module.py` — clean

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Co-authored-by: sentry-junior[bot] <264270552+sentry-junior[bot]@users.noreply.github.com>
Co-authored-by: Neel Shah <6536764+sl0thentr0py@users.noreply.github.com>

Author: sentry-junior[bot]

tests/integrations/django/test_cache_module.py

@@ -1,5 +1,4 @@
 import os
-import random
 import uuid
 
 import pytest
@@ -30,7 +29,7 @@ def use_django_caching(settings):
     settings.CACHES = {
         "default": {
             "BACKEND": "django.core.cache.backends.locmem.LocMemCache",
-            "LOCATION": "unique-snowflake-%s" % random.randint(1, 1000000),
+            "LOCATION": "unique-snowflake-%s" % uuid.uuid4(),
         }
     }
 
@@ -40,7 +39,7 @@ def use_django_caching_with_middlewares(settings):
     settings.CACHES = {
         "default": {
             "BACKEND": "django.core.cache.backends.locmem.LocMemCache",
-            "LOCATION": "unique-snowflake-%s" % random.randint(1, 1000000),
+            "LOCATION": "unique-snowflake-%s" % uuid.uuid4(),
         }
     }
     if hasattr(settings, "MIDDLEWARE"):