Int migration fix (#3323)

* Add fix for stock migration

- Ensure the serial number is not too large when performing migration
- Add unit test for data migration

(cherry picked from commit 661fbf0e3d)

* Add similar fixes for PO and SO migrations

(cherry picked from commit bde23c130c)

* And similar fix for BuildOrder reference field

(cherry picked from commit ca0f4e0031)

* Update unit tests for API plugin mixin class

- API at previous target URL has changed
- Simplier to use the github API as a test case

(cherry picked from commit dfe3172b7d)

* Revert test database name

(cherry picked from commit 53333c29c3)

* Override default URL behaviour for unit test

(cherry picked from commit 2c12a69529)

InvenTree/build/migrations/0032_auto_20211014_0632.py

@@ -24,6 +24,10 @@ def build_refs(apps, schema_editor):
             except Exception:  # pragma: no cover
                 ref = 0
 
+        # Clip integer value to ensure it does not overflow database field
+        if ref > 0x7fffffff:
+            ref = 0x7fffffff
+
         build.reference_int = ref
         build.save()