fix(CI): Use macos-13 for static-builds (#603)

as macos-14 only provide arm builds now.

Related: actions/runner-images#9741

Author: erikmd

.github/workflows/static-builds.yml

@@ -72,7 +72,7 @@ jobs:
   static-bin-macos:
     name: Builds static Macos binaries
     if: ${{ github.event_name != 'schedule' || github.repository == 'ocaml-sf/learn-ocaml' }}
-    runs-on: macos-latest
+    runs-on: macos-13
     env:
       OPAMYES: 1
       OPAMDEPEXTYES: 1