Build with RUBY_DEBUG=1

Seems like a useful thing to do

Author: Earlopain

Dockerfile.template.patch

@@ -1,5 +1,5 @@
 diff --git a/Dockerfile.template b/Dockerfile.template
-index 9f9a685..2a6530d 100644
+index 9f9a685..5134250 100644
 --- a/Dockerfile.template
 +++ b/Dockerfile.template
 @@ -36,7 +36,8 @@ ENV RUBY_DOWNLOAD_SHA256 {{ .sha256.xz }}
@@ -50,3 +50,11 @@ index 9f9a685..2a6530d 100644
  	echo '3ab628a51d92fdf0d2b5835e93564857aea73e0c1de00313864a94a6255cb645 *thread-stack-fix.patch' | sha256sum --check --strict; \
  	patch -p1 -i thread-stack-fix.patch; \
  	rm thread-stack-fix.patch; \
+@@ -203,6 +204,7 @@ RUN set -eux; \
+ 	autoconf; \
+ 	gnuArch="$(dpkg-architecture --query DEB_BUILD_GNU_TYPE)"; \
+ 	./configure \
++		cppflags="-DRUBY_DEBUG=1" \
+ 		--build="$gnuArch" \
+ 		--disable-install-doc \
+ 		--enable-shared \

README.md

@@ -1,6 +1,6 @@
 ![Last successful build](https://img.shields.io/badge/dynamic/json?url=https%3A%2F%2Fapi.github.com%2Frepos%2Fdocker-ruby-nightly%2Fruby%2Factions%2Fworkflows%2Fnightly.yml%2Fruns%3Fstatus%3Dsuccess%26event%3Dschedule&query=%24.workflow_runs%5B0%5D%5B'updated_at'%5D&logo=githubactions&label=Last%20successful%20build) ![Last build status](https://github.com/docker-ruby-nightly/ruby/actions/workflows/nightly.yml/badge.svg)
 
-Builds from https://github.com/docker-library/ruby for daily nightly images.
+Builds from https://github.com/docker-library/ruby for daily nightly images. Configured with `RUBY_DEBUG=1`.
 
 The available variants will mirror the ones from the official images. The tags are structured in the following way:
 * `alpine3.20-nightly-2024-05-27`