ci: do not run tests in parallel by default (#88626)

Jenkinsfile

@@ -6,7 +6,7 @@ pipeline {
     stages {
         stage('Unit Tests') {
             steps {
-                sh 'tox -rv -- --numprocesses 3'
+                sh 'NUMPROCESSES=3 tox -rv'
             }
             post {
                 always {

tox.ini

@@ -13,6 +13,7 @@ setenv =
   CHRONO_SETTINGS_FILE=tests/settings.py
   BRANCH_NAME={env:BRANCH_NAME:}
   SETUPTOOLS_USE_DISTUTILS=stdlib
+  NUMPROCESSES={env:NUMPROCESSES:1}
   coverage: COVERAGE=--junitxml=junit-{envname}.xml --cov-report xml --cov-report html --cov=chrono/ --cov-config .coveragerc
 
 deps =
@@ -44,7 +45,7 @@ allowlist_externals =
 commands =
   ./getlasso3.sh
   python3 setup.py compile_translations
-  py.test -v --dist loadfile {env:COVERAGE:} {posargs:tests/}
+  py.test {posargs:-v --dist loadfile {env:COVERAGE:} --numprocesses={env:NUMPROCESSES:1} tests/}
   codestyle: pre-commit run --all-files --show-diff-on-failure
 
 [testenv:pylint]