Do not store user projects as organization projects (#23353)

A part of https://github.com/go-gitea/gitea/pull/22865

At first, I think we do not need 3 ProjectTypes, as we can check user
type, but it seems that it is not database friendly.

---------

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

models/project/project_test.go

@@ -20,7 +20,7 @@ func TestIsProjectTypeValid(t *testing.T) {
 		typ   Type
 		valid bool
 	}{
-		{TypeIndividual, false},
+		{TypeIndividual, true},
 		{TypeRepository, true},
 		{TypeOrganization, true},
 		{UnknownType, false},