ci: use macos-15-intel runner (macos-13 was retired Dec 2025)

Signed-off-by: Mohammod Al Amin Ashik <maa.ashik00@gmail.com>

Author: its-mash

.github/workflows/release.yml

@@ -88,7 +88,7 @@ jobs:
           - os: macos-latest
             target: aarch64-apple-darwin
             artifact: macos-arm
-          - os: macos-13
+          - os: macos-15-intel
             target: x86_64-apple-darwin
             artifact: macos-intel
 
@@ -290,7 +290,7 @@ jobs:
           SHA_ARM64=$(shasum -a 256 arm64.dmg | cut -d' ' -f1)
           echo "ARM64 SHA256: $SHA_ARM64"
 
-          # x64 DMG (built on macos-13 Intel runner)
+          # x64 DMG (built on macos-15-intel runner)
           HAS_X64=false
           if curl -fSL "${BASE_URL}/McpMux_${VERSION}_x64.dmg" -o x64.dmg 2>/dev/null; then
             SHA_X64=$(shasum -a 256 x64.dmg | cut -d' ' -f1)

.github/workflows/test-release-builds.yml

@@ -21,7 +21,7 @@ jobs:
           - os: macos-latest
             target: aarch64-apple-darwin
             artifact: macos-arm
-          - os: macos-13
+          - os: macos-15-intel
             target: x86_64-apple-darwin
             artifact: macos-intel