ci(github-actions): update legacy CI workflow to fetch phpseclib from GitHub for Composer v1 EOL workaround

Author: nanasess

.github/workflows/ci-legacy.yml

@@ -22,8 +22,9 @@ jobs:
 
             - name: Install dependencies
               run: |
-                  # Force phpseclib 2.x for older PHP versions
+                  # Force phpseclib 2.x for older PHP versions (fetch from GitHub for Composer v1 EOL workaround)
                   if [[ "${{ matrix.php-version }}" < "7.2" ]]; then
+                      composer config repositories.phpseclib vcs https://github.com/phpseclib/phpseclib.git
                       composer require phpseclib/phpseclib:^2.0 --no-update
                   fi
                   composer install --no-interaction --no-cache --prefer-dist