Fix lint issues and improve test suite resilience

- compose.matrix.yml: add trailing newline
- compose.ftp-222*.yml: fix YAML indentation (8->6 spaces)
- entrypoint.sh.tmpl: fix SC2198 ([ -n "$@" ] -> [ $# -gt 0 ])
- All .tmpl files: migrate from {{ env }} to {{ getenv }} for gomplate v5 compat
- uploads.ini.tmpl: add {{- / -}} whitespace trimming, fix double-space typo
- tests/run.sh: only run ShellCheck on *.sh.tmpl files
- tests/test_shell.sh: gracefully skip if shellcheck not installed
- tests/test_templates.sh: remove dead render() function,
  gracefully skip if gomplate not found, use set -a/. for env sourcing
- tests/test_compose_config.sh: validate override files combined
  with compose.yml, skip partial snippets needing more context
- README.md: add test instructions with brew install

entrypoint.sh.tmpl

@@ -1,13 +1,13 @@
 #!/bin/bash
 
-{{ if (env "PHP_EXTENSIONS") }}
-docker-php-ext-install {{ env "PHP_EXTENSIONS" }}
+{{ if (getenv "PHP_EXTENSIONS") }}
+docker-php-ext-install {{ getenv "PHP_EXTENSIONS" }}
 {{ end }}
 
 curl -z /usr/local/bin/wp -o /usr/local/bin/wp https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar
 chmod +x /usr/local/bin/wp
 
-{{ if eq (env "ENABLE_COMPOSER") "1" }}
+{{ if eq (getenv "ENABLE_COMPOSER") "1" }}
 mkdir -p /var/www/.composer
 chown www-data:www-data /var/www/.composer /var/www/html/composer
 
@@ -19,18 +19,18 @@ rm /tmp/composer-setup.php
 mv /var/www/html/composer.phar /usr/local/bin/composer
 {{ end }}
 
-{{ if eq (env "CORS_ALLOW_ALL") "1" }}
+{{ if eq (getenv "CORS_ALLOW_ALL") "1" }}
 a2enmod headers
 sed -ri -e 's/^([ \t]*)(<\/VirtualHost>)/\1\tHeader set Access-Control-Allow-Origin "*"\n\1\2/g' /etc/apache2/sites-available/*.conf
 {{ end }}
 
-{{ if eq (env "MULTISITE") "enable" }}
+{{ if eq (getenv "MULTISITE") "enable" }}
 export WORDPRESS_CONFIG_EXTRA="$WORDPRESS_CONFIG_EXTRA
 define('WP_CACHE', false);
 define('WP_ALLOW_MULTISITE', true );"
 {{ end }}
 
-{{ if or (eq (env "MULTISITE") "subdomain") (eq (env "MULTISITE") "subfolder") }}
+{{ if or (eq (getenv "MULTISITE") "subdomain") (eq (getenv "MULTISITE") "subfolder") }}
 export WORDPRESS_CONFIG_EXTRA="$WORDPRESS_CONFIG_EXTRA
 define('MULTISITE', true);
 define('SUBDOMAIN_INSTALL', true);
@@ -56,7 +56,7 @@ fi
 
 chown -R --from=root:root www-data:www-data /var/www/html/wp-content/
 
-if [ -n "$@" ]; then
+if [ $# -gt 0 ]; then
 	"$@"
 fi