Use JDK 8 in CI (Fixes: #40005)

1 job for master in 1 minute and 18 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test
failed test #19934

00:01:18

 
Name Stage Failure
failed
test Test
    [javac]                                 ^
[javac] 100 errors

BUILD FAILED
/builds/tpo/metrics/collector/src/build/java/base.xml:140: Compile failed; see the compiler error output for details.

Total time: 3 seconds
Cleaning up file based variables
ERROR: Job failed: exit code 1