CI: use macos-15 to build the binaries

Github EOLed the macOS 13 Intel runner and only
supports Intel on macOS 15 from now on.

Let's also use macOS 15 for the Apple Silicon build.

.github/workflows/ci.yml

@@ -138,8 +138,8 @@ jobs:
               {"os": "ubuntu-24.04", "python-version": "3.12", "toxenv": "py312-fuse3"},
               {"os": "ubuntu-24.04", "python-version": "3.13", "toxenv": "py313-fuse3"},
               {"os": "ubuntu-24.04", "python-version": "3.14", "toxenv": "py314-fuse3"},
-              {"os": "macos-13", "python-version": "3.11", "toxenv": "py311-none", "binary": "borg-macos-13-x86_64-gh"},
-              {"os": "macos-14", "python-version": "3.11", "toxenv": "py311-none", "binary": "borg-macos-14-arm64-gh"}
+              {"os": "macos-15-intel", "python-version": "3.11", "toxenv": "py311-none", "binary": "borg-macos-15-x86_64-gh"},
+              {"os": "macos-15", "python-version": "3.11", "toxenv": "py311-none", "binary": "borg-macos-15-arm64-gh"}
             ]
           }'
         ) }}

docs/binaries/00_README.txt

@@ -34,8 +34,8 @@ Binaries built on GitHub servers
 borg-linux-glibc235-x86_64-gh Linux AMD/Intel (built on Ubuntu 22.04 LTS with glibc 2.35)
 borg-linux-glibc235-arm64-gh  Linux ARM (built on Ubuntu 22.04 LTS with glibc 2.35)
 
-borg-macos-14-arm64-gh        macOS Apple Silicon (built on macOS 14 w/o FUSE support)
-borg-macos-13-x86_64-gh       macOS Intel (built on macOS 13 w/o FUSE support)
+borg-macos-15-arm64-gh        macOS Apple Silicon (built on macOS 15 w/o FUSE support)
+borg-macos-15-x86_64-gh       macOS Intel (built on macOS 15 w/o FUSE support)
 
 borg-freebsd-14-x86_64-gh     FreeBSD AMD/Intel (built on FreeBSD 14)