Lower swift-tools-version to 6.0; drop setup-xcode step

6.0 covers all features used; avoids Xcode 26 beta on CI which ships
with Swift tools 6.2.4, lower than the previous 6.3 requirement.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kaishin

.github/workflows/release.yml

@@ -14,10 +14,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: maxim-lobanov/setup-xcode@v1
-        with:
-          xcode-version: latest-stable
-
       - name: Extract version
         run: echo "VERSION=${GITHUB_REF_NAME#v}" >> $GITHUB_ENV
 

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version: 6.3
+// swift-tools-version: 6.0
 
 import PackageDescription