[check.yml] Update MacOS runner and re-enable MacOS precommit action

The path of the `sed` binary on MacOS has changed going from
Intel (macos-13) to M1 (macos-15).

Author: tkoeppe

.github/workflows/check.yml

@@ -18,25 +18,24 @@ jobs:
       matrix:
         cfg:
           - { name: 'Linux', os: 'ubuntu-24.04' }
-          # - { name: 'MacOS', os: 'macos-13' }
+          - { name: 'MacOS', os: 'macos-15' }
 
     steps:
       - name: checkout
         uses: actions/checkout@v4
 
       - name: install GNU tools
-        if: matrix.cfg.os == 'macos-13'
+        if: matrix.cfg.os == 'macos-15'
         run: |
           brew install gnu-sed
-          echo "/usr/local/opt/gnu-sed/libexec/gnubin" >> ${GITHUB_PATH}
+          echo "/opt/homebrew/opt/gnu-sed/libexec/gnubin" >> ${GITHUB_PATH}
 
       - name: check-source.sh
         run: ../tools/check-source.sh
 
       - name: update brew
-        if: matrix.cfg.os == 'macos-13'
-        run: |
-          brew update
+        if: matrix.cfg.os == 'macos-15'
+        run: brew update
 
       - name: update-apt-cache
         if: matrix.cfg.os == 'ubuntu-24.04'
@@ -47,7 +46,7 @@ jobs:
         run: sudo apt-get install latexmk texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended lmodern
 
       - name: install (MacOS)
-        if: matrix.cfg.os == 'macos-13'
+        if: matrix.cfg.os == 'macos-15'
         run: |
           brew install basictex
           eval "$(/usr/libexec/path_helper)"
@@ -60,7 +59,7 @@ jobs:
         run: make quiet
 
       - name: make (MacOS)
-        if: matrix.cfg.os == 'macos-13'
+        if: matrix.cfg.os == 'macos-15'
         run: make full
 
       - name: check-output.sh