ci: skip actions/cache on self-hosted runners (#11986)

cargo registry/target and docker-image caches are already local on a
persistent self-hosted runner; the save/restore pass is pure overhead
(the setup-go cache-save stall on awscli-tests was the same pattern).
Gate every actions/cache step on runner.environment == 'github-hosted'.

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.github/workflows/rust_binaries_dev.yml

@@ -46,6 +46,7 @@ jobs:
         uses: dtolnay/rust-toolchain@stable
 
       - name: Cache cargo registry and target
+        if: runner.environment == 'github-hosted'
         uses: actions/cache@v6
         with:
           path: |
@@ -114,6 +115,7 @@ jobs:
           targets: ${{ matrix.target }}
 
       - name: Cache cargo registry and target
+        if: runner.environment == 'github-hosted'
         uses: actions/cache@v6
         with:
           path: |