Upgrade all macOS Intel workflow runners to macOS 15 (#15840)

Motivation:
GitHub has deprecated the macOS 13 runners and will be removing them.
Details in actions/runner-images#13046

Modification:
Replace the runner OS for all Intel Mac builds with macos-15-intel.

Result:
MacOS builds now run on the latest and last version of MacOS that will
have Intel support.

Author: normanmaurer

.github/workflows/ci-deploy.yml

@@ -74,7 +74,7 @@ jobs:
       matrix:
         include:
           - setup: macos-x86_64
-            os: macos-13
+            os: macos-15-intel
           - setup: macos-aarch64
             os: macos-15
 

.github/workflows/ci-pr.yml

@@ -134,7 +134,7 @@ jobs:
       matrix:
         include:
           - setup: macos-x86_64
-            os: macos-13
+            os: macos-15-intel
           - setup: macos-aarch64
             os: macos-15
 

.github/workflows/ci-release.yml

@@ -259,7 +259,7 @@ jobs:
       matrix:
         include:
           - setup: macos-x86_64
-            os: macos-13
+            os: macos-15-intel
           - setup: macos-aarch64
             os: macos-15