API crash on /api/v1/projects/ with non-numeric organisation query parameter

[emyller]

Acceptance criteria

• URL matching or view logic prevents an error with a proper 4xx response.

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Sentry Issue: FLAGSMITH-API-5NT

ValueError: invalid literal for int() with base 10: 'A60ZG9cp5WC53RRZHDkIlUiWuAL57Jhi'
  File "django/db/models/fields/__init__.py", line 2128, in get_prep_value
    return int(value)

ValueError: Field 'id' expected a number but got 'A60ZG9cp5WC53RRZHDkIlUiWuAL57Jhi'.
...
  File "projects/views.py", line 103, in get_queryset
    queryset = queryset.filter(organisation__id=organisation_id)

Contributes to #6809

[sentry]

Sentry Issue: FLAGSMITH-API-5NT