GH-46240: [Release][Packaging] Fix a bug that existing APT repositories' metadata are lost (#46287)

### Rationale for this change

APT repositories' metadata for 20.0.0 RC 2 don't have existing packages such as 19.0.1 packages. We should keep metadata for existing packages and append metadata for new packages.

### What changes are included in this PR?

* Fix paths for existing metadata
* Fix pattern for detecting new packages
  * This is for apache/arrow-adbc#2769

### Are these changes tested?

Yes. I tested this with ADBC 18 RC 0.

### Are there any user-facing changes?

No.
* GitHub Issue: #46240

Authored-by: Sutou Kouhei <[email protected]>
Signed-off-by: Sutou Kouhei <[email protected]>

Author: kou

dev/release/binary-task.rb

@@ -1649,7 +1649,10 @@ def define_apt_rc_tasks
             rm_rf(pool_dir, verbose: verbose?)
             mkdir_p(pool_dir, verbose: verbose?)
             source_dir_prefix = "#{artifacts_dir}/#{distribution}-#{code_name}"
-            Dir.glob("#{source_dir_prefix}-*/*") do |path|
+            # apache/arrow uses debian-bookworm-{amd64,arm64} but
+            # apache/arrow-adbc uses debian-bookworm. So the following
+            # glob must much both of them.
+            Dir.glob("#{source_dir_prefix}*/*") do |path|
               base_name = File.basename(path)
               package_name = ENV["DEB_PACKAGE_NAME"]
               if package_name.nil? or package_name.empty?
@@ -1686,16 +1689,17 @@ def define_apt_rc_tasks
 
         desc "Download dists/ for RC APT repositories"
         task :download do
-          apt_distributions.each do |distribution|
+          apt_targets.each do |distribution, code_name, component|
             not_checksum_pattern = /.+(?<!\.asc|\.sha512)\z/
-            base_distribution_dir = "#{base_dir}/#{distribution}"
+            base_distribution_dir =
+              "#{base_dir}/#{distribution}/dists/#{code_name}"
             pattern = not_checksum_pattern
             download_distribution(:artifactory,
                                   distribution,
                                   base_distribution_dir,
                                   :base,
                                   pattern: pattern,
-                                  prefix: "dists")
+                                  prefix: "dists/#{code_name}")
           end
         end