unset XDG_HOME_CONFIG as gitea manages configuration locations (#33067)

unset XDG_CONFIG_HOME early to enable gitea to manage git configuration.
simple error checking to satisfy the linting. Closes #33039

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/setting/config_env.go

@@ -166,3 +166,8 @@ func EnvironmentToConfig(cfg ConfigProvider, envs []string) (changed bool) {
 	}
 	return changed
 }
+
+// InitGiteaEnvVars initilises the environment for gitea
+func InitGiteaEnvVars() {
+	_ = os.Unsetenv("XDG_CONFIG_HOME") // unset if set as HOME is managed by gitea
+}