ci: comment macOS, empty Windows icon path, fix Android keystore preset

Three follow-ups from run #12:

- export-desktop: comment out the macOS matrix entry. The preset
  is still missing in export_presets.cfg; the entry can be
  uncommented once the macOS preset is added in the Godot editor.

- export Windows: `application/icon` referenced
  res://releases/windows/project.ico, which has never been in the
  repo (releases/windows/ holds only .keep). Godot rejected the
  export with "Invalid icon path". Cleared the field in both
  WindowsDebug and WindowsTesting presets — Godot falls back to
  its built-in icon.

- export-android: Godot validation requires all three of
  keystore/debug{,_user,_password} to be set together (or all
  empty). The keystore step only patched keystore/debug and left
  the other two empty, triggering
  "Either Debug Keystore, Debug User AND Debug Password must be
  configured OR none of them". Patch all three now.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

export_presets.cfg

@@ -230,7 +230,7 @@ codesign/timestamp_server_url=""
 codesign/digest_algorithm=1
 codesign/description=""
 codesign/custom_options=PoolStringArray(  )
-application/icon="res://releases/windows/project.ico"
+application/icon=""
 application/file_version=""
 application/product_version=""
 application/company_name=""
@@ -296,7 +296,7 @@ codesign/timestamp_server_url=""
 codesign/digest_algorithm=1
 codesign/description=""
 codesign/custom_options=PoolStringArray(  )
-application/icon="res://releases/windows/project.ico"
+application/icon=""
 application/file_version=""
 application/product_version=""
 application/company_name=""