Make "two PHP per Drupal" more explicit (#300)

This embeds that constraint directly in the `jq` code, which also simplifies current and future conditionals to be simply "which versions support (or do not support) this PHP" and the "limit to two" is done by the code instead.

Author: tianon

versions.sh

@@ -110,21 +110,25 @@ for version in "${versions[@]}"; do
 			# TODO adjust this in a way that is easier to manage over time (semi-automatic variant combinations, for example, based on availability/supported status of upstream PHP images)
 			phpVersions: (
 				# https://www.drupal.org/docs/system-requirements/php-requirements
-				[
+				[ limit(2;
+					# we support up to two PHP versions per Drupal version
+
 					# Drupal 11.3+ supports PHP 8.5
 					if env.version | IN("10.5", "10.6", "11.2") then empty else
 						"8.5"
 					end,
+
 					# Drupal 11.1+ and 10.4+ support PHP 8.4
 					"8.4",
+
 					# Drupal 11.3+ and 10.6+ recommend PHP 8.4; keep 8.3 for 'existing' builds
 					# https://github.com/docker-library/drupal/pull/299
 					# https://www.drupal.org/project/drupal/releases/10.6.0#platform
 					# https://www.drupal.org/project/drupal/releases/11.3.0#platform
-					if env.version | IN("10.5", "10.6", "11.2") then
-						"8.3"
-					else empty end
-				]
+					"8.3",
+
+					empty
+				) ]
 			),
 			variants: [
 				"trixie",