Conda Update: macos-26-intel legs fail on a frozen Intel Miniconda (conda 25.7.0) and a 404 upload binary #2044

The macos-26-intel legs of Conda Update fail on main. They failed in run 39206429076 on 2026-10-19, and again in run 39812667872 today. They have not passed since they were added (#1822, #1825). create-release.yml's conda job has the same setup, so the next release will fail the same way.

Cause. The step Conda environment creation and activation sets no installer, so on osx-64 setup-miniconda downloads Miniconda3-latest-MacOSX-x86_64.sh. That installer has been frozen since 2025-08-25 and ships conda 25.7.0, which auto-update-conda: false then keeps. This causes three failures:

1. Python 3.11 and 3.12, in Install conda build tools: PluginError: Conflicting plugins found for post_solves. conda-forge's conda-content-trust ≥0.3.0 registers the signature-verification hook, and conda older than 26.3 still has its own built-in copy.
2. Python 3.14: LibMambaUnsatisfiableError. conda 25.7.0 has no py314 build.
3. Python 3.13 and 3.15, in Upload conda packages to Anaconda: upload-package@v0.3.1 downloads ana-darwin-x86_64, which returns 404. ana-darwin-arm64 is 200, and v0.3.1 is the latest release.

Fix for 1 and 2. In both workflows, pass miniforge-version: latest on the Intel legs. Miniforge 26.7.2 ships osx-64 with a conda newer than 26.3. I'm starting this fix now.

Decision needed for 3. On the Intel legs, the upload has to stop using the action. Options:

• (a) Recommended: on Intel legs only, upload with the anaconda-client CLI (anaconda upload --skip-existing) from the build env, and keep the action everywhere else.
• (b) Use the CLI on every leg.
• (c) Build osx-64 but upload it from a non-Intel job.