[CI] Bump actions/upload-artifact from 3 to 4

The dependabot bump of download-artifact must have a corresponding
bump for upload-artifact, since v3 and v4 are incompatible. See
https://github.com/actions/toolkit/blob/main/packages/artifact/docs/faq.md#which-versions-of-the-artifacts-packages-are-compatible

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

Author: feltech

.github/build_openassetio/action.yml

@@ -24,7 +24,7 @@ runs:
         cmake -G Ninja -S . -DOPENASSETIO_ENABLE_C="ON" -B build
         cmake --build build
         cmake --install build
-    - uses: actions/upload-artifact@v3
+    - uses: actions/upload-artifact@v4
       with:
         name: OpenAssetIO Build
         path: openassetio-checkout/build/dist

.github/build_openassetio_mediacreation/action.yml

@@ -28,7 +28,7 @@ runs:
         cmake -G Ninja -S . -B build
         cmake --build build
         cmake --install build
-    - uses: actions/upload-artifact@v3
+    - uses: actions/upload-artifact@v4
       with:
         name: OpenAssetIO MediaCreation Build
         path: openassetio-mediacreation-checkout/build/dist