[2.2.x] Fixed #30870 -- Fixed showing that RunPython operations are irreversible by migrate --plan.

Thanks Hasan Ramezani for the initial patch and Kyle Dickerson for the
report.

Backport of 06d34aab7c from master.

tests/migrations/test_migrations_plan/0005_fifth.py

@@ -0,0 +1,22 @@
+from django.db import migrations
+
+
+def grow_tail(x, y):
+    pass
+
+
+def feed(x, y):
+    """Feed salamander."""
+    pass
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('migrations', '0004_fourth'),
+    ]
+
+    operations = [
+        migrations.RunPython(migrations.RunPython.noop),
+        migrations.RunPython(grow_tail),
+        migrations.RunPython(feed, migrations.RunPython.noop),
+    ]