ci: temporarily disable all cache upload/download

Disable ccache/bazel cache transfer for debugging: prepare-ccache download
and artifact upload in main.yml, and the prebuilt-ccache artifact download
plus the two GitHub-native actions/cache steps in build.yml. prepare-ccache
job remains as an empty needs-gate so build jobs still run.

.github/workflows/build.yml

@@ -267,6 +267,7 @@ jobs:
         compression-level: 9
 
     - name: Get prebuilt ccache (downloaded once by prepare-ccache)
+      if: false
       uses: actions/download-artifact@v8
       with:
         name: ccache-binary
@@ -306,6 +307,7 @@ jobs:
           ${{ inputs.android_version }}-${{ inputs.kernel_version }}.${{ steps.extract.outputs.sublevel }}-
 
     - name: Cache ccache (GitHub Native)
+      if: false
       uses: actions/cache@v6
       with:
         path: /home/runner/.ccache
@@ -316,6 +318,7 @@ jobs:
           ccache-
 
     - name: Cache bazel-cache (GitHub Native)
+      if: false
       uses: actions/cache@v6
       with:
         path: /home/runner/.cache/bazel

.github/workflows/main.yml

@@ -91,6 +91,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Download custom ccache once
+        if: false
         run: |
           set -uo pipefail
           echo "::group::Download ccache"
@@ -111,6 +112,7 @@ jobs:
           fi
           echo "::endgroup::"
       - name: Upload ccache artifact
+        if: false
         uses: actions/upload-artifact@v7
         with:
           name: ccache-binary