Upgrade from macos-13 to macos-15-intel

`macos-13` has been deprecated and the CI is failing due to that, actions/runner-images#13046

Author: ArchangelX360

.github/workflows/main.yml

@@ -20,7 +20,7 @@ jobs:
             target: x86_64-apple-darwin
             nobgt: 0
             no_tests: 1
-            tag: macos-13
+            tag: macos-15-intel
           - name: x86_64-unknown-linux-gnu (nightly)
             target: x86_64-unknown-linux-gnu
             nobgt: 0