Prevent primary key update on migration (#26192)

Fixes #25918

The migration fails on MSSQL because xorm tries to update the primary
key column. xorm prevents this if the column is marked as auto
increment:

c622cdaf89/internal/statements/update.go (L38-L40)

I think it would be better if xorm would check for primary key columns
here because updating such columns is bad practice. It looks like if
that auto increment check should do the same.

fyi @lunny

models/migrations/v1_20/v250.go

@@ -20,7 +20,7 @@ func ChangeContainerMetadataMultiArch(x *xorm.Engine) error {
 	}
 
 	type PackageVersion struct {
-		ID           int64  `xorm:"pk"`
+		ID           int64  `xorm:"pk autoincr"`
 		MetadataJSON string `xorm:"metadata_json"`
 	}