Bump actions/checkout from 3 to 4 (#212)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/cygwin.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       fail-fast: false
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set up Cygwin
         uses: egor-tensin/setup-cygwin@v4 # https://github.com/marketplace/actions/install-cygwin

.github/workflows/mingw.yml

@@ -20,7 +20,7 @@ jobs:
     env:
       BUILD_PATH: build_space
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: set up python
         uses: actions/setup-python@v4

.github/workflows/python-tests.yml

@@ -20,18 +20,18 @@ jobs:
 
     steps:
     - name: Check out ApprovalTests.cpp
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         path: ApprovalTests/ApprovalTests.cpp
 
     - name: Check out ApprovalTests.cpp.StarterProject
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: approvals/ApprovalTests.cpp.StarterProject
         path: ApprovalTests/ApprovalTests.cpp.StarterProject
 
     - name: Check out claremacrae fork of conan-center-index
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: claremacrae/conan-center-index
         path: conan/conan-center-index-claremacrae
@@ -42,7 +42,7 @@ jobs:
         git remote add upstream https://github.com/conan-io/conan-center-index.git
    
     - name: Check out llewellyn's fork of vcpkg
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: isidore/vcpkg
         path: ApprovalTests/vcpkg