load default PHP versions from dokuwiki repo

We do not want to hardcode the default versions for stable and master,
instead we pull them from the testLinux.yaml workflow. This way we have
a canonical place to define those versions.

Author: splitbrain

.github/actions/dokuenv/action.yml

@@ -17,5 +17,5 @@ outputs:
   maxphp:
     description: 'The maximum PHP version compatible with the extension, if set. Otherwise empty.'
 runs:
-  using: 'node16'
+  using: 'node20'
   main: 'index.js'

.github/actions/phpmatrix/action.yml

@@ -8,5 +8,5 @@ outputs:
   minphp:
     description: 'The minimum PHP version supported'
 runs:
-  using: 'node16'
+  using: 'node20'
   main: 'index.js'

.github/actions/phpmatrix/index.js

@@ -1,4 +1,5 @@
 const core = require('@actions/core');
+const yaml = require('js-yaml');
 const dwUtils = require('../dokuwikiUtils');
 
 /**
@@ -15,16 +16,31 @@ function toNumberString(num) {
     }
 }
 
-async function main() {
-    /**
-     * these are the default versions for each branch
-     * @fixme ideally we would load this from the dokuwiki repo
-     */
+/**
+ * Load the PHP versions to test against by default from the dokuwiki repo
+ *
+ * @returns {Promise<{stable: *[], master: *[]}>}
+ */
+async function fetchPHPVersions() {
     const defaults = {
-        stable: [7.2, 7.3, 7.4, 8.0, 8.1, 8.2],
-        master: [7.4, 8.0, 8.1, 8.2],
+        stable: [],
+        master: [],
     }
 
+    for (const [branch, ] of Object.entries(defaults)) {
+        const url = `https://raw.githubusercontent.com/dokuwiki/dokuwiki/${branch}/.github/workflows/testLinux.yml`
+        const response = await fetch(url);
+        const body = await response.text()
+        const doc = yaml.load(body);
+        defaults[branch] = doc.jobs.run.strategy.matrix['php-versions'];
+    }
+    console.log('Default PHP Versions:', defaults);
+    return defaults;
+}
+
+async function main() {
+    const defaults = await fetchPHPVersions();
+
     const matrix = {
         stable: {
             'dokuwiki-branch': ['stable'],