[ci] Run pmd-regression-tester with multiple threads

Also build the baseline with multiple threads.

.ci/inc/regression-tester.inc

@@ -50,6 +50,7 @@ function regression_tester_uploadBaseline() {
         --patch-branch "${baseline_branch}" \
         --patch-config ./pmd/.ci/files/all-regression-rules.xml \
         --list-of-project ./pmd/.ci/files/project-list.xml --html-flag \
+        --threads "$(nproc)" \
         --error-recovery
     pushd target/reports || { echo "Directory 'target/reports' doesn't exist"; exit 1; }
     BRANCH_FILENAME="${baseline_branch/\//_}"

Dangerfile

@@ -2,6 +2,7 @@ require 'pmdtester'
 require 'time'
 require 'logger'
 require 'fileutils'
+require 'etc'
 
 @logger = Logger.new(STDOUT)
 
@@ -16,6 +17,7 @@ def get_args(base_branch, autogen = TRUE, patch_config = './pmd/.ci/files/all-re
    '--keep-reports',
    '--error-recovery',
    '--baseline-download-url', 'https://pmd-code.org/pmd-regression-tester/',
+   '--threads', Etc.nprocessors.to_s,
    # '--debug',
    ]
 end