Bump GitHub actions checkout to v4

Author: bowenszhu

.github/workflows/Documentation.yml

@@ -11,7 +11,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@latest
         with:
           version: '1.10'

.github/workflows/Downstream.yml

@@ -26,7 +26,7 @@ jobs:
           - {user: SciML, repo: ModelOrderReduction.jl, group: All}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.julia-version }}

.github/workflows/benchmark_pr.yml

@@ -13,7 +13,7 @@ jobs:
         runs-on: ubuntu-latest
 
         steps:
-            - uses: actions/checkout@v2
+            - uses: actions/checkout@v4
             - uses: julia-actions/setup-julia@v1
               with:
                 version: "1"

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - run: |