jzmq: FTBFS with OpenJDK 21 due to unsupported javac source/target level 7

The package jzmq ftbfs with default Java 21.
The relevant part of the build log:
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make[2]: Entering directory '/<<PKGBUILDDIR>>/src/main/c++'
javac -source 1.7 -target 1.7 -d . -h . ../java/org/zeromq/EmbeddedLibraryTools.java ../java/org/zeromq/ZAuth.java ../java/org/zeromq/ZContext.java ../java/org/zeromq/ZDispatcher.java ../java/org/zeromq/ZFrame.java ../java/org/zeromq/ZLoop.java ../java/org/zeromq/ZMQ.java ../java/org/zeromq/ZMQException.java ../java/org/zeromq/ZMQForwarder.java ../java/org/zeromq/ZMQQueue.java ../java/org/zeromq/ZMQStreamer.java ../java/org/zeromq/ZMsg.java ../java/org/zeromq/ZThread.java
warning: [options] bootstrap class path not set in conjunction with -source 7
error: Source option 7 is no longer supported. Use 8 or later.
error: Target option 7 is no longer supported. Use 8 or later.
make[2]: *** [Makefile:877: zmq.jar] Error 2
make[2]: Leaving directory '/<<PKGBUILDDIR>>/src/main/c++'
make[1]: *** [Makefile:403: all-recursive] Error 1
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
dh_auto_build: error: make -j1 returned exit code 2
make: *** [debian/rules:14: build-arch] Error 25
dpkg-buildpackage: error: debian/rules build-arch subprocess returned exit status 2
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