use gradle 8.4 (#2869)

diff --git a/build/docker/ubuntu-focal/Dockerfile b/build/docker/ubuntu-focal/Dockerfile
index 1f30573..a6121fa 100644
--- a/build/docker/ubuntu-focal/Dockerfile
+++ b/build/docker/ubuntu-focal/Dockerfile
@@ -162,7 +162,7 @@
       haxelib setup --always /usr/share/haxe/lib && \
       haxelib install --always hxcpp 2>&1 > /dev/null
 
-ENV GRADLE_VERSION="8.0.2"
+ENV GRADLE_VERSION="8.4"
 RUN apt-get install -y --no-install-recommends \
       `# Java dependencies` \
       ant \
@@ -171,7 +171,7 @@
       openjdk-17-jdk-headless && \
       `# Gradle` \
       wget https://services.gradle.org/distributions/gradle-$GRADLE_VERSION-bin.zip -q -O /tmp/gradle-$GRADLE_VERSION-bin.zip && \
-      (echo "ff7bf6a86f09b9b2c40bb8f48b25fc19cf2b2664fd1d220cd7ab833ec758d0d7  /tmp/gradle-$GRADLE_VERSION-bin.zip" | sha256sum -c -) && \
+      (echo "3e1af3ae886920c3ac87f7a91f816c0c7c436f276a6eefdb3da152100fef72ae  /tmp/gradle-$GRADLE_VERSION-bin.zip" | sha256sum -c -) && \
       unzip -d /tmp /tmp/gradle-$GRADLE_VERSION-bin.zip && \
       mv /tmp/gradle-$GRADLE_VERSION /usr/local/gradle && \
       ln -s /usr/local/gradle/bin/gradle /usr/local/bin