docs: fix documentation generation (#383)

Fix documentation generation

This corrects a mistake I made when I proposed the changes for doc generation: we don't actually generate docs for `macos-xcodebuild`! The error was masked, because once docs are in S3 they don't get deleted by subsequent builds not generating them. I.e. the existing docs for `main` were simply slowly getting more and more outdated.

A recent change on our end exposed this issue.

.spi.yml

@@ -3,9 +3,10 @@ builder:
   configs:
   - platform: ios
     scheme: "ParseSwift (iOS)"
+  - platform: macos-spm
+    documentation_targets: [ParseSwift]
   - platform: macos-xcodebuild
     scheme: "ParseSwift (macOS)"
-    documentation_targets: ["ParseSwift (macOS)"]
   - platform: macos-xcodebuild-arm
     scheme: "ParseSwift (macOS)"
   - platform: tvos