Cygwin: CI: bump actions/checkout from v3 to v5

There were two major version bumps:

- v3 -> v4: new runs using Node.JS v20 instead of v16
- v4 -> v5: now runs using Node.JS v24 instead of v20

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/cygwin.yml

@@ -24,7 +24,7 @@ jobs:
       HAS_SSH_KEY: ${{ secrets.SSH_KEY != '' }}
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v5
 
     # install build tools
     - name: Install build tools
@@ -111,7 +111,7 @@ jobs:
       run: |
         icacls . /inheritance:r
         icacls . /grant Administrators:F
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v5
 
     # install cygwin and build tools
     - name: Install Cygwin