Disable minimal size requirement for ed25519 keys

debexpo previously checked that ed25519 keys had a length of 256. Since
libgcrypt-1.9.0, this value has been updated to 255. Instead of
adjusting the size, the minimal requirement for ed25519 keys have been
dropped since all keys have a unique length anyway.

See: https://dev.gnupg.org/rCdb7b2c591004868abedbc2c19d3bb2efebf8529d
See: https://lists.gnupg.org/pipermail/gnupg-users/2021-September/065454.html

debexpo/keyring/migrations/0004_set_ecc_size_to_zero.py

+#   0004_set_ecc_size_to_zero.py - Set ECC minimum size to zero
+#
+#   This file is part of debexpo
+#   https://salsa.debian.org/mentors.debian.net-team/debexpo
+#
+#   Copyright © 2021 Baptiste Beauplat <lyknode@debian.org>
+#
+#   Permission is hereby granted, free of charge, to any person
+#   obtaining a copy of this software and associated documentation
+#   files (the "Software"), to deal in the Software without
+#   restriction, including without limitation the rights to use,
+#   copy, modify, merge, publish, distribute, sublicense, and/or sell
+#   copies of the Software, and to permit persons to whom the
+#   Software is furnished to do so, subject to the following
+#   conditions:
+#
+#   The above copyright notice and this permission notice shall be
+#   included in all copies or substantial portions of the Software.
+#
+#   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+#   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+#   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+#   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+#   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+#   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+#   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+#   OTHER DEALINGS IN THE SOFTWARE.
+
+from django.db import migrations
+
+
+def set_ecc_size_to_zero(apps, schema_editor):
+    set_ecc_size(apps, schema_editor, 0)
+
+
+def revert_set_ecc_size_to_zero(apps, schema_editor):  # pragma: no cover
+    set_ecc_size(apps, schema_editor, 256)
+
+
+def set_ecc_size(apps, schema_editor, size):
+    GPGAlgo = apps.get_model('keyring', 'GPGAlgo')
+
+    algo = GPGAlgo.objects.get(name='ed25519')
+    algo.minimal_size_requirement = size
+    algo.full_clean()
+    algo.save()
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ('keyring', '0003_fingerprint_uniqueness',),
+    ]
+
+    operations = [
+        migrations.RunPython(set_ecc_size_to_zero, revert_set_ecc_size_to_zero),
+    ]