ci: fix retired macos-13 image (#2905)

Author: anmonteiro

.github/workflows/esy-ci.yml

@@ -22,7 +22,7 @@ jobs:
       matrix:
         os:
           - ubuntu-latest
-          - macos-13
+          - macos-15-intel
           - windows-latest
 
         ocaml-compiler:

.github/workflows/nix-build.yml

@@ -43,10 +43,10 @@ jobs:
     strategy:
       matrix:
         setup:
-          - {ocaml-version: '5_3', os: macos-13}
-          - {ocaml-version: '4_14', os: macos-14}
-          - {ocaml-version: '5_3', os: macos-14}
-          - {ocaml-version: '5_4', os: macos-14}
+          - {ocaml-version: '5_3', os: macos-15-intel}
+          - {ocaml-version: '4_14', os: macos-latest}
+          - {ocaml-version: '5_3', os: macos-latest}
+          - {ocaml-version: '5_4', os: macos-latest}
     runs-on: ${{ matrix.setup.os }}
     steps:
     - uses: actions/checkout@v4

.github/workflows/opam-ci.yml

@@ -23,8 +23,8 @@ jobs:
           - {ocaml-compiler: '4.14.x', os: ubuntu-latest}
           - {ocaml-compiler: 'ocaml-base-compiler.5.3.0', os: ubuntu-latest}
           - {ocaml-compiler: 'ocaml-base-compiler.5.4.0', os: ubuntu-latest}
-          - {ocaml-compiler: 'ocaml-base-compiler.5.4.0', os: macos-13}
-          - {ocaml-compiler: 'ocaml-base-compiler.5.4.0', os: macos-14}
+          - {ocaml-compiler: 'ocaml-base-compiler.5.4.0', os: macos-15-intel}
+          - {ocaml-compiler: 'ocaml-base-compiler.5.4.0', os: macos-latest}
             # looks like setup-ocaml@v3 can only run actions on windows for
             # OCaml >= 4.13
             # https://github.com/ocaml/setup-ocaml/issues/822#issuecomment-2215525942