[copilot] free up disk space by removing pre-installed Android SDK (#10629)

Context: #10629

The Copilot GitHub Actions runner was running out of disk space with 76% 
used (54G/72G) after checkout, leaving only 18GB free for builds.

Changes:
- Remove `/usr/local/lib/android` before checkout (~12GB pre-installed SDK/NDK)
- Add `fetch-depth: 1` for shallow clones of main repo and submodules

Results:
- Disk usage after checkout: 59% (42G/72G) with 30GB free
- Saved 12GB total, providing sufficient space for build operations
- Build caches already redirected to /mnt (66GB available) via #10610

Author: jonathanpeppers

.github/workflows/copilot-setup-steps.yml

@@ -15,10 +15,16 @@ jobs:
       NUGET_SCRATCH: /mnt/nuget/scratch
 
     steps:
+    - name: Free up disk space
+      run: |
+        # Remove pre-installed Android SDK/NDK (~10GB) since we download our own specific versions
+        sudo rm -rf /usr/local/lib/android
+
     - name: Checkout repository
       uses: actions/checkout@v4
       with:
         submodules: recursive
+        fetch-depth: 1
 
     - name: Log disk space (after checkout)
       uses: ./.github/workflows/log-disk-space