[3.0.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_commands.py

@@ -371,6 +371,28 @@ class MigrateTests(MigrationTestBase):
                 '    Raw SQL operation -> IRREVERSIBLE\n',
                 out.getvalue()
             )
+            out = io.StringIO()
+            call_command('migrate', 'migrations', '0005', plan=True, stdout=out, no_color=True)
+            # Operation is marked as irreversible only in the revert plan.
+            self.assertEqual(
+                'Planned operations:\n'
+                'migrations.0005_fifth\n'
+                '    Raw Python operation\n'
+                '    Raw Python operation\n'
+                '    Raw Python operation -> Feed salamander.\n',
+                out.getvalue()
+            )
+            call_command('migrate', 'migrations', '0005', verbosity=0)
+            out = io.StringIO()
+            call_command('migrate', 'migrations', '0004', plan=True, stdout=out, no_color=True)
+            self.assertEqual(
+                'Planned operations:\n'
+                'migrations.0005_fifth\n'
+                '    Raw Python operation -> IRREVERSIBLE\n'
+                '    Raw Python operation -> IRREVERSIBLE\n'
+                '    Raw Python operation\n',
+                out.getvalue()
+            )
         finally:
             # Cleanup by unmigrating everything: fake the irreversible, then
             # migrate all to zero.

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),
+    ]