[CI] Use actions/checkout v4

Part of OpenAssetIO/OpenAssetIO#1351. Now that the `openassetio-build`
container can support nodejs 20 (because glibc is new enough) we can
update `actions/checkout`.

This was an attempt to fix an error in GitHub CI

```
fatal: detected dubious ownership in repository at '/__w/OpenAssetIO-Test-CMake/OpenAssetIO-Test-CMake'
```

But it didn't work. See subsequent commit for workaround.

Signed-off-by: David Feltell <[email protected]>

Author: feltech

.github/build_openassetio/action.yml

@@ -11,7 +11,7 @@ runs:
   using: "composite"
   steps:
     - name: Checkout OpenAssetIO
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: OpenAssetIO/OpenAssetIO
         path: openassetio-checkout

.github/build_openassetio_mediacreation/action.yml

@@ -11,7 +11,7 @@ runs:
   using: "composite"
   steps:
     - name: Checkout OpenAssetIO-Mediacreation
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: OpenAssetIO/OpenAssetIO-MediaCreation
         path: openassetio-mediacreation-checkout

.github/workflows/test.yml

@@ -18,7 +18,7 @@ jobs:
     container:
       image: ghcr.io/openassetio/openassetio-build
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Build
         uses: ./.github/build_openassetio
 
@@ -28,7 +28,7 @@ jobs:
     container:
       image: ghcr.io/openassetio/openassetio-build
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Build
         uses: ./.github/build_openassetio_mediacreation
 
@@ -39,7 +39,7 @@ jobs:
       image: aswf/ci-base:2024
     needs: [build-openassetio, build-openassetio-mediacreation]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Get OpenAssetIO
         uses: actions/download-artifact@v3
@@ -72,7 +72,7 @@ jobs:
       image: ghcr.io/openassetio/openassetio-build
     needs: [build-openassetio-mediacreation]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Get OpenAssetIO-MediaCreation
         uses: actions/download-artifact@v3
@@ -105,7 +105,7 @@ jobs:
       image: aswf/ci-base:2024
     needs: [build-openassetio]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Get OpenAssetIO
         uses: actions/download-artifact@v3
@@ -139,7 +139,7 @@ jobs:
     container:
       image: ghcr.io/openassetio/openassetio-build
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install Traitgen
         run: |