[macOS CI] Use conda>=25.3.0 floor in setup-binary-builds to fix osx-arm64 nightly builds

The base miniconda env's Python differs per runner: macOS runners moved to
python=3.14 (pinned), while Windows runners are still on python=3.9. `conda
install -y conda=25.3.0` is unsatisfiable on the macOS base env because conda
25.3.0 has no Python 3.14 build (py314 builds start at 26.1.0), so every
osx-arm64 nightly wheel build has failed in `setup-binary-builds` since
2026-07-09 with:

    LibMambaUnsatisfiableError: package conda-25.3.0-py310hca03da5_0 requires
    python >=3.10,<3.11.0a0 ... Currently pinned specs: - python=3.14

But no single exact conda version covers both base Pythons (py39 support ends
at 25.9.1; py314 starts at 26.1.0). Replace the exact pin with a floor
(conda>=25.3.0) so each platform's solver resolves to the newest conda its
base Python allows: 25.9.1 on Windows (py3.9), 26.5.3 on macOS (py3.14) and
Linux. This runs in the base env before the target env is created, which is
why all Python versions failed identically and only osx-arm64 was affected.

Author: atalman

.github/actions/setup-binary-builds/action.yml

@@ -129,7 +129,11 @@ runs:
           set -euxo pipefail
           CONDA_ENV="${RUNNER_TEMP}/conda_environment_${GITHUB_RUN_ID}"
           export CONDA_EXTRA_PARAM=""
-          conda install -y conda=25.3.0
+          # The base conda env's Python differs per runner (Windows: 3.9,
+          # macOS: 3.14), and no single conda version has builds for both
+          # (py39 support ends at 25.9.1; py314 starts at 26.1.0). Use a floor
+          # so each platform resolves to the newest conda its base Python allows.
+          conda install -y "conda>=25.3.0"
 
           # shellcheck disable=SC2153
           case $PYTHON_VERSION in