Quote the load check so /bin/sh can parse it

The check used escaped double quotes around a Ruby interpolation, which
the pipeline's /bin/sh rejected with "Unterminated quoted string". Single
quotes outside, plain concatenation inside — no escapes left to misread.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.woodpecker.yaml

@@ -14,4 +14,4 @@ steps:
       - gem build bbs.gemspec
       - echo "==> Load check"
       - gem install --no-document ./bbs-*.gem
-      - ruby -e "require 'bbs'; puts \"BBS betoltve, #{BBS.constants.size} konstans\""
+      - ruby -e 'require "bbs"; puts "BBS betoltve, " + BBS.constants.size.to_s + " konstans"'