Factorize deps list

.github/workflows/ci.yml

   pull_request:
     branches: [ master ]
 
+env:
+  deps: libpcaudio-dev libsonic-dev ronn kramdown
+
 jobs:
   build:
 
       if: matrix.arch == 'x86-32'
     - name: dependencies-apt
       if: matrix.os == 'ubuntu-latest'
-      run: sudo apt-get update && sudo apt-get install libpcaudio-dev libsonic-dev ronn kramdown ${{ matrix.deps }} ${{ matrix.archdeps }}
+      run: sudo apt-get update && sudo apt-get install ${{ env.deps }} ${{ matrix.deps }} ${{ matrix.archdeps }}
     - name: dependencies-brew
       if: matrix.os == 'macos-latest'
       run: brew install libtool automake ronn OJFord/homebrew-formulae/kramdown ${{ matrix.archdeps }} ;
         run: sudo dpkg --add-architecture i386
         if: matrix.arch == 'x86-32'
       - name: dependencies
-        run: sudo apt-get update && sudo apt-get install libpcaudio-dev libsonic-dev ronn kramdown reprotest ${{ matrix.archdeps }}
+        run: sudo apt-get update && sudo apt-get install ${{ env.deps }} reprotest ${{ matrix.archdeps }}
       - name: autoconf
         run: ./autogen.sh ; chmod -x INSTALL m4/*.m4
       - name: run
     steps:
       - uses: actions/checkout@v2
       - name: dependencies
-        run: sudo apt-get update && sudo apt-get install libpcaudio-dev libsonic-dev ronn kramdown
+        run: sudo apt-get update && sudo apt-get install ${{ env.deps }}
       - name: autoconf
         run: ./autogen.sh ; chmod -x INSTALL m4/*.m4
       - name: configure