ci: run fewer macOS runs (#2810)

* ci: run fewer macOS runs

* fix branch name for the nix pipeline

.github/workflows/nix-build.yml

@@ -4,7 +4,7 @@ on:
   pull_request:
   push:
    branches:
-     - main
+     - master
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
@@ -42,9 +42,8 @@ jobs:
     strategy:
       matrix:
         setup:
-          - {ocaml-version: '5_2', os: macos-13}
+          - {ocaml-version: '5_3', os: macos-13}
           - {ocaml-version: '4_14', os: macos-14}
-          - {ocaml-version: '5_2', os: macos-14}
           - {ocaml-version: '5_3', os: macos-14}
     runs-on: ${{ matrix.setup.os }}
     steps:

.github/workflows/opam-ci.yml

@@ -23,10 +23,8 @@ jobs:
           - {ocaml-compiler: '4.14.x', os: ubuntu-latest}
           - {ocaml-compiler: 'ocaml-base-compiler.5.3.0~alpha1', os: ubuntu-latest}
           - {ocaml-compiler: '4.06.x', os: macos-13}
-          - {ocaml-compiler: '4.10.x', os: macos-13}
-          - {ocaml-compiler: '4.12.x', os: macos-13}
-          - {ocaml-compiler: '4.14.x', os: macos-13}
           - {ocaml-compiler: 'ocaml-base-compiler.5.3.0~alpha1', os: macos-13}
+          - {ocaml-compiler: 'ocaml-base-compiler.5.3.0~alpha1', os: macos-14}
             # 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