Replace deprecated macos-13 GHA image with latest x64 image (#5649)

`macos-13` will soon be removed from github actions
[[src](https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/)].
We are replacing it in our nightlies and release workflows with
`macos-15-intel` which according to
actions/runner-images#13045 is now available
for building on x64.

However, let's keep in mind that "Apple has discontinued support for the
x86_64 (Intel) architecture. GitHub will no longer support this
architecture on macOS after the macOS 15 runner image is retired in Fall
2027."
[[src](https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/#notice-of-macos-x86_64-intel-architecture-deprecation)]

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TYPE: NO_HISTORY

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Co-authored-by: Theodore Tsirpanis <[email protected]>

Author: ypatia

.github/workflows/nightly-test.yml

@@ -78,7 +78,7 @@ jobs:
             triplet: x64-linux
           - os: windows-2022
             triplet: x64-windows
-          - os: macos-13
+          - os: macos-15-intel
             triplet: x64-osx
             deployment-target: 13
           - os: macos-latest

.github/workflows/release.yml

@@ -62,7 +62,7 @@ jobs:
             triplet: arm64-linux-release
             manylinux: quay.io/pypa/manylinux_2_28_aarch64
           - platform: macos-x86_64
-            os: macos-13
+            os: macos-latest
             cmake_args: -DCMAKE_OSX_ARCHITECTURES=x86_64
             MACOSX_DEPLOYMENT_TARGET: 11
             triplet: x64-osx-release