Update checkout action to v4, cleanup the workflow

checkout@v2 is deprecated

.github/workflows/main.yml

@@ -1,31 +1,17 @@
-# This is a basic workflow to help you get started with Actions
-
 name: CI
 
-# Controls when the action will run. 
 on:
-  # Triggers the workflow on push or pull request events but only for the master branch
   push:
     branches: [ '*' ]
   pull_request:
     branches: [ master ]
-
-  # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
 
-# A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
-  # This workflow contains a single job called "build"
   melodic:
-    # The type of runner that the job will run on
     runs-on: ubuntu-latest
-
-    # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
-      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@v2
-
-      # Runs a set of commands using the runners shell
+      - uses: actions/checkout@v4
       - name: Build for ROS Melodic
         env:
           NATIVE_DOCKER: ros:melodic-ros-base
@@ -39,7 +25,7 @@ jobs:
   noetic:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Build for ROS Noetic
         env:
           NATIVE_DOCKER: ros:noetic-ros-base