Fix #2506

Updates:
- AST extension is no longer installed for unsupported PHP versions

workspace/Dockerfile

@@ -585,10 +585,13 @@ ARG AST_VERSION=1.0.3
 ENV AST_VERSION ${AST_VERSION}
 
 RUN if [ ${INSTALL_AST} = true ]; then \
+    # AST extension requires PHP 7.0.0 or newer
+    if [ $(php -r "echo PHP_MAJOR_VERSION;") != "5" ]; then \
         # Install AST extension
         printf "\n" | pecl -q install ast-${AST_VERSION} && \
         echo "extension=ast.so" >> /etc/php/${LARADOCK_PHP_VERSION}/mods-available/ast.ini && \
         phpenmod -v ${LARADOCK_PHP_VERSION} -s cli ast \
+    ;fi \
 ;fi
 
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