Fix individual tests (addition to #15802) (#15818)

* Decouple TestAction_GetRepoLink and TestSizedAvatarLink.

* Load database for TestCheckGPGUserEmail.

* Load database for TestMakeIDsFromAPIAssigneesToAdd.

* Load database for TestGetUserIDsByNames and TestGetMaileableUsersByIDs.

* Load database for TestUser_ToUser.

* Load database for TestRepository_EditWikiPage.

* Include AppSubURL in test.

* Prevent panic with empty slice.

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

services/wiki/wiki_test.go

@@ -162,6 +162,8 @@ func TestRepository_AddWikiPage(t *testing.T) {
 }
 
 func TestRepository_EditWikiPage(t *testing.T) {
+	assert.NoError(t, models.PrepareTestDatabase())
+
 	const newWikiContent = "This is the new content"
 	const commitMsg = "Commit message"
 	repo := models.AssertExistsAndLoadBean(t, &models.Repository{ID: 1}).(*models.Repository)