Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/build.yml

@@ -19,7 +19,7 @@ jobs:
       uses: actions/setup-python@v3
       with:
         python-version: 3.7
-    - uses: actions/checkout@v2.4.0
+    - uses: actions/checkout@v4.1.1
     - uses: julia-actions/setup-julia@v1
       with:
         version: '1.4.1'

.github/workflows/tests.yml

@@ -19,7 +19,7 @@ jobs:
       uses: actions/setup-python@v3
       with:
         python-version: 3.7
-    - uses: actions/checkout@v2.4.0
+    - uses: actions/checkout@v4.1.1
     - uses: julia-actions/setup-julia@v1
       with:
         version: '1.4.1'
@@ -59,7 +59,7 @@ jobs:
         uses: actions/setup-python@v3
         with:
           python-version: 3.7
-      - uses: actions/checkout@v2.4.0
+      - uses: actions/checkout@v4.1.1
       - uses: julia-actions/setup-julia@v1
         with:
           version: '1.4.1'