ARM linux CI jobs fail when using torch 2.9 rc wheels

🐛 Describe the bug

ARM Linux CI jobs are failing on the release/1.0 branch when using prebuilt PyTorch + domain packages. This appears to be due to the PyTorch packages requiring glibcxx 3.4.30. The existing ARM Linux images we use have 3.4.29.

This is a known problem with Conda on Ubuntu 22.04 (see https://github.com/pytorch/pytorch/issues/105248) and there is a workaround in install_conda.sh:
https://github.com/pytorch/executorch/blob/181ed4dd2adffaeaf158da5bfb9192a0e6199f1f/.ci/docker/common/install_conda.sh#L59-L62

However, this workaround is not used on ARM Linux because it apparently breaks the CI jobs (introduced in https://github.com/pytorch/executorch/pull/12068):
https://github.com/pytorch/executorch/blob/181ed4dd2adffaeaf158da5bfb9192a0e6199f1f/.ci/docker/common/install_conda.sh#L74-L78

ImportError: /opt/conda/envs/py_3.10/bin/../lib/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /opt/conda/envs/py_3.10/lib/python3.10/site-packages/executorch/extension/pybindings/_portable_lib.cpython-310-aarch64-linux-gnu.so)

From https://github.com/pytorch/executorch/actions/runs/18111201043/job/51550387476

We need to figure out what the proper fix is, perhaps updating the libcxx version in the docker image build or somewhere else? As a short-term fix, I'm installing a newer version with Conda in https://github.com/pytorch/executorch/pull/14677.

Versions

release/1.0 - commit 3854f4b36

Start with .ci/docker/common/install_conda.sh, comparing the workaround at lines 59-62 with the ARM Linux path at lines 74-78. Review the referenced GitHub Actions job and the short-term approach in pull request 14677 to identify a fix that does not break ARM CI. Done means ARM Linux jobs on release/1.0 can install and import the torch 2.9 RC wheels successfully.