Use text field to store version range string

Version range can be very long (>5000 char) for some advisory.

Signed-off-by: Keshav Priyadarshi <git@keshav.space>

Author: keshav-space

vulnerabilities/migrations/0100_remove_advisoryv2_affecting_packages_and_more.py

@@ -1,4 +1,4 @@
-# Generated by Django 4.2.22 on 2025-07-22 09:15
+# Generated by Django 4.2.22 on 2025-07-28 18:30
 
 from django.db import migrations, models
 import django.db.models.deletion
@@ -38,18 +38,16 @@ class Migration(migrations.Migration):
                 ),
                 (
                     "affecting_vers",
-                    models.CharField(
+                    models.TextField(
                         blank=True,
                         help_text="VersionRange expression for package vulnerable to this impact.",
-                        max_length=500,
                     ),
                 ),
                 (
                     "fixed_vers",
-                    models.CharField(
+                    models.TextField(
                         blank=True,
                         help_text="VersionRange expression for packages fixing the vulnerable package in this impact.",
-                        max_length=500,
                     ),
                 ),
                 (