Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/build_demo.yml

@@ -12,7 +12,7 @@ jobs:
 
     steps:
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set image tag
         run: |

.github/workflows/build_deploy_staging.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set variables
         run: |

.github/workflows/remove_st_after_pr.yml

@@ -13,7 +13,7 @@ jobs:
 
     steps:
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Get pull request reference number
         run: |

.github/workflows/ruby.yml

@@ -21,7 +21,7 @@ jobs:
     continue-on-error: ${{ endsWith(matrix.ruby, 'head') || matrix.ruby == 'debug' }}
     steps:
 
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}