GH-45478: [CI][C++] Drop support for Ubuntu 20.04

[kou]

Rationale for this change

Ubuntu 20.04 will read EOL on 2025-05.

What changes are included in this PR?

Remove jobs that use Ubuntu 20.04 or replace them with Ubuntu 22.04.

Are these changes tested?

Yes.

Are there any user-facing changes?

No.

• GitHub Issue: [CI][C++] Drop support for Ubuntu 20.04 #45478

[kou]

@github-actions crossbow submit -g cpp

[github-actions]

⚠️ GitHub issue #45478 has been automatically assigned in GitHub to PR creator.

[github-actions]

while constructing a mapping
  in "<unicode string>", line 200, column 3:
      conan-minimum:
      ^ (line: 200)
found duplicate key "test-ubuntu-24.04-cpp" with value "{'ci': 'github', 'template': 'docker-tests/github.linux.yml', 'params': {'env': {'CLANG_TOOLS': 15, 'LLVM': 15, 'UBUNTU': 24.04}, 'image': 'ubuntu-cpp'}}" (original value: "{'ci': 'github', 'template': 'docker-tests/github.linux.yml', 'params': {'env': {'UBUNTU': '24.04'}, 'image': 'ubuntu-cpp'}}")
  in "<unicode string>", line 2755, column 3:
      test-ubuntu-24.04-cpp:
      ^ (line: 2755)

To suppress this check see:
    http://yaml.readthedocs.io/en/latest/api.html#duplicate-keys

The Archery job run can be found at: https://github.com/apache/arrow/actions/runs/13299355605

[kou]

@github-actions crossbow submit -g cpp

[github-actions]

Revision: 2db5d69

Submitted crossbow builds: ursacomputing/crossbow @ actions-5cb949d02e

Task	Status
example-cpp-minimal-build-static
example-cpp-minimal-build-static-system-dependency
example-cpp-tutorial
test-alpine-linux-cpp
test-build-cpp-fuzz
test-conda-cpp
test-conda-cpp-valgrind
test-cuda-cpp-ubuntu-22.04-cuda-11.7.1
test-debian-12-cpp-amd64
test-debian-12-cpp-i386
test-fedora-39-cpp
test-ubuntu-22.04-cpp
test-ubuntu-22.04-cpp-20
test-ubuntu-22.04-cpp-bundled
test-ubuntu-22.04-cpp-emscripten
test-ubuntu-22.04-cpp-no-threading
test-ubuntu-24.04-cpp
test-ubuntu-24.04-cpp-bundled-offline
test-ubuntu-24.04-cpp-gcc-13-bundled
test-ubuntu-24.04-cpp-gcc-14
test-ubuntu-24.04-cpp-minimal-with-formats
test-ubuntu-24.04-cpp-thread-sanitizer

[raulcd]

LGTM The failures on CI are unrelated

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit a21147b.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 48 possible false positives for unstable benchmarks that are known to sometimes produce them.