ci: build the osx-64 installer on a native Intel runner (#1020)

* ci: build the osx-64 installer on a native Intel runner

macos-latest is arm64 now, so packing the x86_64 osx-64 conda environment
there runs its Python under Rosetta, which aborts conda pack intermittently
with "rosetta error: unable to mmap __TEXT" (#1018). Pinning just the osx-64
leg to macos-15-intel, the last x86_64 image, runs the build natively and
avoids the emulation. The osx-arm64 leg stays on macos-latest since it is
native there.

I confirmed the macos-15-intel label and its availability window (through
August 2027) with Claude Code before making the change.

* ci: use macos-26-intel, the newest Intel image

macos-latest-intel is not a real label (GitHub only ships macos-15-intel and
macos-26-intel; -latest is arm64), and macos-26-intel is newer than the -15
one, so it tracks macOS 26 like the arm64 legs and lasts longer before the
x86_64 retirement.

Verified the available Intel labels against the runner-images list and the
GitHub-hosted runners docs with Claude Code.

Author: notluquis

.github/workflows/publish.yml

@@ -34,7 +34,11 @@ jobs:
       matrix:
         cfg:
         - { platform: linux-64, platform_name: Linux x64,  os: ubuntu-latest, build_platform: linux-64, conda_platform: linux-64 }
-        - { platform: osx-64, platform_name: macOS x64, os: macos-latest, build_platform: osx-64, conda_platform: osx-64 }
+        # Native Intel runner: macos-latest is arm64, and packing the osx-64
+        # env there runs its x86_64 Python under Rosetta, which aborts conda
+        # pack intermittently (#1018). macos-26-intel is the newest x86_64
+        # image (GitHub offers no macos-latest-intel; -latest is arm64 only).
+        - { platform: osx-64, platform_name: macOS x64, os: macos-26-intel, build_platform: osx-64, conda_platform: osx-64 }
         - { platform: osx-arm64, platform_name: macOS arm64, os: macos-latest, build_platform: osx-64, conda_platform: osx-arm64 }
         - { platform: win-64, platform_name: Windows x64, os: windows-latest, build_platform: win-64, conda_platform: win-64 }