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.

.cirrus.yml

@@ -253,38 +253,3 @@ macos_task:
     - make V=1 test-ci
   install_script:
     - sudo -H make V=1 install
-
-linux_musl_task:
-  skip: "changesIncludeOnly(
-    '**/CMakeLists.txt',
-    '.azure-pipelines.yml',
-    '.circleci/**',
-    '.github/**',
-    'appveyor.yml',
-    'CMake/**',
-    'packages/**',
-    'plan9/**',
-    'projects/**',
-    'winbuild/**'
-    )"
-  name: Linux MUSL
-  container:
-    image: alpine:3.18
-    memory: 800M
-
-  env:
-    CIRRUS_CLONE_DEPTH: 10
-    MAKEFLAGS: -j 3
-
-  pkginstall_script:
-    - 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
-  configure_script:
-    - autoreconf -fi
-    - ./configure --enable-warnings --enable-debug --enable-websockets --with-ssl --with-libssh2 --with-libidn2 --with-gssapi --enable-ldap --with-libpsl
-  compile_script:
-    - make V=1 && make V=1 examples && make -C tests V=1
-  test_script:
-    # TODO: ssh tests don't work, likely because we're running as root
-    - USER=nobody make V=1 test-ci
-  install_script:
-    - make V=1 install

.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')