feat(updates): add AtomGit update download source

apps/desktop/src/components/editor/EditorSettingsDialog.vue

@@ -996,7 +996,7 @@ function onLocaleChange(v: any) {
 }
 
 function onUpdateDownloadSourceChange(v: any) {
-  if (v === "official" || v === "cnb") editUpdateDownloadSource.value = v;
+  if (v === "official" || v === "cnb" || v === "atomgit") editUpdateDownloadSource.value = v;
 }
 
 function setSidebarObjectDisplay(value: "grouped" | "simple") {
@@ -3659,6 +3659,7 @@ onUnmounted(cleanupPreviewEditor);
                     <SelectContent>
                       <SelectItem value="official">{{ t("settings.updateDownloadSourceOfficial") }}</SelectItem>
                       <SelectItem value="cnb">{{ t("settings.updateDownloadSourceCnb") }}</SelectItem>
+                      <SelectItem value="atomgit">{{ t("settings.updateDownloadSourceAtomgit") }}</SelectItem>
                     </SelectContent>
                   </Select>
                 </div>