CI: move the Alpine build from Cirrus to GHA

Cirrus is reducing their free tier to next to nothing, so we must move
builds elsewhere.

.github/workflows/linux.yml

@@ -160,6 +160,10 @@ jobs:
           # Docker Hub image that `container-job` executes in
           container: 'andy5995/slackware-build-essential:15.0'
 
+        - name: Alpine MUSL
+          configure: --enable-debug --enable-websockets --with-ssl --with-libssh2 --with-libidn2 --with-gssapi --enable-ldap --with-libpsl
+          container: 'alpine:3.18'
+
     steps:
     - if: matrix.build.container == null
       run: |
@@ -168,6 +172,11 @@ jobs:
         sudo python3 -m pip install impacket
       name: 'install prereqs and impacket'
 
+    - if: startsWith(matrix.build.container, 'alpine')
+      run: |
+        apk add --no-cache build-base autoconf automake libtool perl openssl-dev libssh2-dev zlib-dev brotli-dev zstd-dev libidn2-dev openldap-dev heimdal-dev libpsl-dev py3-impacket py3-asn1 py3-six py3-pycryptodomex perl-time-hires openssh stunnel sudo
+      name: 'install dependencies'
+
     - uses: actions/checkout@v3
 
     - if: contains(matrix.build.install_steps, 'gcc-11')