ci: Drop support for macOS 13 & 14 mirroring y-scope/clp#1130.

Author: davidlion

.github/workflows/build.yaml

@@ -31,8 +31,6 @@ jobs:
     strategy:
       matrix:
         os:
-          - "macos-13"
-          - "macos-14"
           - "macos-15"
           - "ubuntu-22.04"
           - "ubuntu-24.04"

.github/workflows/lint.yml

@@ -33,9 +33,5 @@ jobs:
       - name: "Install task"
         run: "npm install -g @go-task/cli"
 
-      - if: "matrix.os == 'macos-15'"
-        name: "Install coreutils (for md5sum)"
-        run: "brew install coreutils"
-
       - name: "Run lint task"
         run: "task lint:check"