ci: point the worker builds at the vendored protoc

lance's crates compile protos of their own and look for a protoc, so every job
that builds the worker failed at lance-encoding's build script. They read
PROTOC, so pointing it at the binary protoc-bin-vendored already puts in the
registry serves them without a system package - one less apt call on the way
to a release, and the same version everywhere.

Claude-Session: https://claude.ai/code/session_01Rkp1Mw5E89Jp6dzJFYiMrm

.github/workflows/container_dev.yml

@@ -61,6 +61,18 @@ jobs:
           restore-keys: |
             rust-docker-dev-${{ matrix.target }}-
 
+      # lance's build scripts compile their own protos and look for a protoc.
+      # Point them at the one protoc-bin-vendored ships, which seaweed-worker's
+      # own build already uses, so no job depends on a system package and every
+      # build sees the same version.
+      - name: Use the vendored protoc
+        run: |
+          cd seaweed-worker
+          cargo fetch
+          protoc=$(find ~/.cargo/registry/src -path '*protoc-bin-vendored-linux-x86_64*/bin/protoc' | head -1)
+          test -x "$protoc" || { echo "no vendored protoc in the registry" >&2; exit 1; }
+          echo "PROTOC=$protoc" >> "$GITHUB_ENV"
+
       - name: Build normal variant
         env:
           SEAWEEDFS_COMMIT: ${{ github.sha }}