ci: 更新获取 commit message 的命令

- 修复了获取 commit message 时的语法错误
- 使用 PowerShell 兼容的命令格式

Author: spark

.github/workflows/main.yml

@@ -33,7 +33,7 @@ jobs:
 
       - name: Get commit message
         run: |
-          commit_message=$(git log -1 --pretty=format:"# [%an  %ad] # %s %b")
+          $commit_message = & git log -1 --pretty=format:"# [%an  %ad] # %s %b"
           echo "Commit message: $commit_message"
 
       - name: Build wails