Fix JSON serialization error in get_installed_apps()

[dantte-lp]

Fixes: #20993

Summary

This PR adds a defensive check in get_installed_apps() to skip VERSION attributes that are neither tuples nor strings, preventing JSON serialization errors in the /api/status/ endpoint.

The Problem:

Some packages (like django-health-check using setuptools-scm) define their VERSION attribute as a type placeholder at runtime rather than an actual version value:

# In django-health-check's _version.py (generated by setuptools-scm)
VERSION_TUPLE: Tuple[int, int, int] = object  # This is <class 'object'> at runtime!

When get_installed_apps() encounters this, it includes <class 'object'> in the dictionary, which fails JSON serialization.

The Fix:

Add an elif branch to skip non-serializable version types:

if type(version) is tuple:
    version = '.'.join(str(n) for n in version)
elif not isinstance(version, str):
    # Skip non-serializable version types (e.g. setuptools-scm placeholders)
    continue

This is a minimal, defensive change that:

• Maintains existing behavior for tuple and string versions
• Gracefully handles edge cases from third-party packages
• Has no impact on correctly-behaving packages

Testing:

Verified fix resolves the issue with django-health-check 3.20.0 installed.