Switch to AWS' dual-stack S3 URLs (#213)

The default AWS S3 URLs only support IPv4, whereas the dual-stack
URLs support both IPv4 and IPv6:
https://docs.aws.amazon.com/AmazonS3/latest/API/ipv6-access.html
https://docs.aws.amazon.com/AmazonS3/latest/API/dual-stack-endpoints.html

By switching to the dual-stack URLs, it means systems that support IPv6
will now use it instead of IPv4, which is helpful in IPv6 environments where
IPv4 traffic has to fall back to being routed via NAT gateways (which has
performance and ingress cost implications).

See also:
https://salesforce-internal.slack.com/archives/C01R6FJ738U/p1770827176094169

GUS-W-21348093.

Author: edmorley

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Changed the S3 URLs used for downloads to use AWS' dual-stack (IPv6 compatible) endpoint. ([#213](https://github.com/heroku/heroku-buildpack-clojure/pull/213))
 
 ## [v95] - 2026-02-18
 

lib/openjdk.sh

@@ -12,7 +12,7 @@ function openjdk::install_openjdk_via_jvm_common_buildpack() {
 
 	# Legacy behaviour for customers and testing code can override the download location of the heroku/jvm buildpack
 	# with JVM_COMMON_BUILDPACK for testing and debugging purposes.
-	local jvm_common_buildpack_tarball_url="${JVM_COMMON_BUILDPACK:-https://buildpack-registry.s3.us-east-1.amazonaws.com/buildpacks/heroku/jvm.tgz}"
+	local jvm_common_buildpack_tarball_url="${JVM_COMMON_BUILDPACK:-https://buildpack-registry.s3.dualstack.us-east-1.amazonaws.com/buildpacks/heroku/jvm.tgz}"
 
 	local jvm_common_buildpack_tarball_path
 	jvm_common_buildpack_tarball_path=$(mktemp)