ci: disable sccache preprocessor cache mode

The preprocessor cache has produced 0 hits in every observed CI run
because pip's per-run build-isolation overlay path lands in -I flags
and sccache hashes raw compiler arguments without basedir stripping.
The lookup overhead is ~20 min per Linux wheel job; until the
underlying issue is fixed, just stop enabling it.

See #2220.

Author: leofang

.github/workflows/build-wheel.yml

@@ -55,7 +55,6 @@ jobs:
           curl -fsSL "https://github.com/rapidsai/sccache/releases/latest/download/sccache-$(uname -m)-unknown-linux-musl.tar.gz" \
             | sudo tar -C /usr/local/bin -xvzf - --wildcards --strip-components=1 -x '*/sccache'
           echo "SCCACHE_PATH=/usr/local/bin/sccache" >> "$GITHUB_ENV"
-          echo "SCCACHE_GHA_USE_PREPROCESSOR_CACHE_MODE=true" >> "$GITHUB_ENV"
 
       # xref: https://github.com/orgs/community/discussions/42856#discussioncomment-7678867
       - name: Adding addtional GHA cache-related env vars
@@ -190,7 +189,6 @@ jobs:
             ACTIONS_RESULTS_URL=${{ env.ACTIONS_RESULTS_URL }}
             ACTIONS_CACHE_URL=${{ env.ACTIONS_CACHE_URL }}
             ACTIONS_CACHE_SERVICE_V2=${{ env.ACTIONS_CACHE_SERVICE_V2 }}
-            SCCACHE_GHA_USE_PREPROCESSOR_CACHE_MODE=${{ env.SCCACHE_GHA_USE_PREPROCESSOR_CACHE_MODE }}
             SCCACHE_DIR=/host/${{ env.SCCACHE_DIR }}
             SCCACHE_CACHE_SIZE=${{ env.SCCACHE_CACHE_SIZE }}
           CIBW_ENVIRONMENT_WINDOWS: >
@@ -261,7 +259,6 @@ jobs:
             ACTIONS_RESULTS_URL=${{ env.ACTIONS_RESULTS_URL }}
             ACTIONS_CACHE_URL=${{ env.ACTIONS_CACHE_URL }}
             ACTIONS_CACHE_SERVICE_V2=${{ env.ACTIONS_CACHE_SERVICE_V2 }}
-            SCCACHE_GHA_USE_PREPROCESSOR_CACHE_MODE=${{ env.SCCACHE_GHA_USE_PREPROCESSOR_CACHE_MODE }}
             SCCACHE_DIR=/host/${{ env.SCCACHE_DIR }}
             SCCACHE_CACHE_SIZE=${{ env.SCCACHE_CACHE_SIZE }}
           CIBW_ENVIRONMENT_WINDOWS: >
@@ -518,7 +515,6 @@ jobs:
             ACTIONS_RESULTS_URL=${{ env.ACTIONS_RESULTS_URL }}
             ACTIONS_CACHE_URL=${{ env.ACTIONS_CACHE_URL }}
             ACTIONS_CACHE_SERVICE_V2=${{ env.ACTIONS_CACHE_SERVICE_V2 }}
-            SCCACHE_GHA_USE_PREPROCESSOR_CACHE_MODE=${{ env.SCCACHE_GHA_USE_PREPROCESSOR_CACHE_MODE }}
             SCCACHE_DIR=/host/${{ env.SCCACHE_DIR }}
             SCCACHE_CACHE_SIZE=${{ env.SCCACHE_CACHE_SIZE }}
           CIBW_ENVIRONMENT_WINDOWS: >