CI: Improve reusable 'install' action

.github/actions/install/action.yml

@@ -30,24 +30,11 @@ runs:
           run: |
               COMPOSER_ROOT_VERSION=
 
-              COMPOSER_BRANCH_ALIAS="$(php -r "
-                  \$json = json_decode(file_get_contents('./composer.json'), true);
-                  if (\$json !== null) {
-                      if (isset(\$json['extra']['branch-alias']['dev-$GITHUB_REF_NAME'])) {
-                          echo 'dev-$GITHUB_REF_NAME';
-                      }
-                  }
-              ")"
-
-              if [ -z "$COMPOSER_BRANCH_ALIAS" ]; then
-                  PICO_VERSION_PATTERN="$(php -r "
+              if [ -z "$(composer config extra.branch-alias."dev-$GITHUB_REF_NAME")" ]; then
+                  COMPOSER_ROOT_VERSION="$(php -r "
                       require('./lib/Pico.php');
                       echo preg_replace('/\.[0-9]+-dev$/', '.x-dev', Pico::VERSION);
                   ")"
-              fi
-
-              if [ -n "$PICO_VERSION_PATTERN" ]; then
-                  COMPOSER_ROOT_VERSION="$PICO_VERSION_PATTERN"
                   echo "COMPOSER_ROOT_VERSION=$COMPOSER_ROOT_VERSION" | tee -a "$GITHUB_ENV"
               fi