[ci] Build Linux ARM64 thirdparty in GitHub Actions

[hello-stephen]

What changed

• add a native Linux ARM64 matrix entry using GitHub's ubuntu-22.04-arm hosted runner
• select ldb_toolchain_gen_aarch64.sh for the ARM64 job while keeping the existing x86_64 toolchain
• upload both doris-thirdparty-prebuilt-linux-aarch64.tar.xz and the existing compatibility asset doris-thirdparty-prebuild-arm64.tar.xz

Why

Linux ARM64 prebuilds currently depend on an internal ARM machine plus an hourly upload cron, unlike the other three platforms. Public repositories can now use standard native ARM64 GitHub-hosted runners, so the build and publication can live in the same workflow as Linux x86_64 and macOS.

Keeping the legacy asset name avoids breaking existing Doris release jobs and download URLs during the migration.

Validation

• actionlint .github/workflows/build.yml
• YAML parse and git diff --check
• live Linux ARM64 GitHub Actions run will be linked in a follow-up PR comment

[hello-stephen]

Linux ARM64 GitHub Actions validation: passed

The second validation round for commit b05bee4c6352c360901bb57084eb5f146cf5e71a is complete.

• Workflow run: 30803820994
• ARM64 job: 91654674188 — completed / success at 2026-08-03T11:25:28Z
• Runner/toolchain: ubuntu-22.04-arm, native aarch64, using ldb_toolchain_gen_aarch64.sh
• Build log confirms Target system: Linux; Target arch: aarch64 and Finished to build all thirdparties
• Prerelease output and packaged marker both equal 0c01156be7f468ce73a4d903f3f374668e7a7548
• Downloaded canonical archive locally and verified:
  • size: 720086376 bytes
  • SHA256: 69c6f04213d7c13e90ef0e132e77e207eb6824e454641937d5454471bf521d0d
  • contains installed/_doris_thirdparty_commit_
  • contains installed/lib64/libadbc_driver_manager.a
  • contains installed/lib64/libadbc_driver_jni.so

Published assets on the fork's automation release:

Asset	ID	Size	Updated	Digest
doris-thirdparty-prebuilt-linux-aarch64.tar.xz	499974055	720086376	2026-08-03T11:25:22Z	sha256:69c6f04213d7c13e90ef0e132e77e207eb6824e454641937d5454471bf521d0d
doris-thirdparty-prebuild-arm64.tar.xz	499974052	720086376	2026-08-03T11:25:26Z	sha256:69c6f04213d7c13e90ef0e132e77e207eb6824e454641937d5454471bf521d0d

The canonical and compatibility asset names have identical size and GitHub digest, so the existing ARM64 download URL remains compatible. The first-round missing-marker issue is fixed by b05bee4c6352c360901bb57084eb5f146cf5e71a.

Other matrix jobs are independent of this ARM64 validation.