ci(distributions): save DuckDB's objects from the nightly, not every main run

Each save adds a cache entry of a few hundred MB per platform, and saving
from every run on main would churn the repository's cache space and evict
the Cargo git caches other jobs restore. Main now saves from the scheduled
nightly build, and otherwise only when the restore matched no objects for
this DuckDB and its settings, so a first fill or an upgrade still saves.
Other pushes and release builds only restore.

Author: kvlonge

.github/workflows/build-distributions.yml

@@ -193,8 +193,11 @@ jobs:
           key="$(sha256 <<< "${settings}" | cut -c 1-16)"
           echo "DUCKDB_CACHE_KEY=duckdb-objects-v1-${{ matrix.platform.name }}-${key}" >> "${GITHUB_ENV}"
       # Restored on every build, but saved only from main (below), so a release or publish build
-      # never reads objects another branch compiled.
+      # never reads objects another branch compiled. Main saves from the scheduled nightly build, and
+      # otherwise only when no saved objects match this DuckDB and its settings (a first fill or an
+      # upgrade), so the repository's cache space is not spent on a copy per push.
       - name: Restore DuckDB's compiled objects
+        id: duckdb-cache
         if: inputs.prebuilt-run-id == ''
         uses: actions/cache/restore@v4
         with:
@@ -242,10 +245,14 @@ jobs:
         run: '"${CMAKE_C_COMPILER_LAUNCHER}" --stop-server'
       # The manylinux container writes the cache as root, and sccache keeps its files private.
       - name: Give the runner the container's cache files
-        if: inputs.prebuilt-run-id == '' && runner.os == 'Linux'
+        if: >-
+          runner.os == 'Linux' && inputs.prebuilt-run-id == '' && github.ref == 'refs/heads/main'
+          && (github.event_name == 'schedule' || steps.duckdb-cache.outputs.cache-matched-key == '')
         run: sudo chown -R "$(id -u):$(id -g)" .sccache-cache
       - name: Save DuckDB's compiled objects from main
-        if: inputs.prebuilt-run-id == '' && github.ref == 'refs/heads/main'
+        if: >-
+          inputs.prebuilt-run-id == '' && github.ref == 'refs/heads/main'
+          && (github.event_name == 'schedule' || steps.duckdb-cache.outputs.cache-matched-key == '')
         uses: actions/cache/save@v4
         with:
           path: .sccache-cache