fix: change args from let to mut for reassignment compatibility

Fixes Nu parser error:
  Error: nu::parser::assignment_requires_mutable_variable
  '' needs to be a mutable variable to support append ['--fix']
  Use 'mut args' instead of 'let args'

Author: shenxianpeng

action.yml

@@ -463,7 +463,7 @@ runs:
         $env.UV_INSTALL_DIR = $action_path | path join 'bin'
         $env.UV_CACHE_DIR = $env.RUNNER_TEMP | path join 'cpp-linter-action-cache'
 
-        let args = [
+        mut args = [
           '--style=${{ inputs.style }}'
           '--extensions=${{ inputs.extensions }}'
           '--tidy-checks=${{ inputs.tidy-checks }}'