ci-mercurial-core: install libfuzzer-9-dev

This is expected to let the test using the fuzzer to pass.
3 jobs for topic/default/libfuzzer-9-dev in 14 minutes and 4 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Check
passed shellcheck #152167

00:00:20

 
  Image Build 0
passed build:base #152168

00:08:06

 
  Image Build 1
failed build:mercurial-core #152169

00:05:36

 
Name Stage Failure
failed
build:mercurial-core Image Build 1
Reading package lists...
Reading package lists...
Building dependency tree...
Reading state information...
E: Unable to locate package libfuzzer-9-dev
error building image: error building stage: failed to execute command: waiting for process to exit: exit status 100
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1