racket: bump debian image, racket version (#8200)

* racket: bump debian to bullseye

* racket: bump Racket to 8.9

* racket: drop PLT_INCREMENTAL_GC=1

This marginally improves performance.

frameworks/Racket/racket/racket.dockerfile

@@ -1,4 +1,4 @@
-FROM debian:stretch-slim AS debian
+FROM debian:bullseye-slim AS debian
 
 ARG DEBIAN_FRONTEND=noninteractive
 ARG TERM=linux
@@ -11,7 +11,7 @@ RUN echo 'APT::Get::Install-Recommends "false";' > /etc/apt/apt.conf.d/00-genera
 
 FROM debian AS racket
 
-ARG RACKET_VERSION=8.6
+ARG RACKET_VERSION=8.9
 
 RUN apt-get update -q \
     && apt-get install --no-install-recommends -q -y \

frameworks/Racket/racket/scripts/run

@@ -4,6 +4,4 @@ set -euo pipefail
 
 echo never > /sys/kernel/mm/transparent_hugepage/enabled
 redis-server /racket/config/redis.conf &
-
-export PLT_INCREMENTAL_GC=1
 /racket/bin/app --host 0.0.0.0 --port 8080