Fix iOS workflow.

XCode version 15.0-beta is no longer available and causes all tests to break.
Use version 15.0.1 instead.

Author: IVLIVS-III

.github/workflows/dart.yml

@@ -38,7 +38,7 @@ jobs:
     steps:
       - uses: maxim-lobanov/setup-xcode@v1
         with:
-          xcode-version: '15.0-beta'
+          xcode-version: '15.0-1'
       - uses: actions/checkout@v2
       - uses: actions/setup-java@v1
         with: