Backport PR pandas-dev#51902: Re-enable parallel builds in CI

Author: WillAyd

.circleci/setup_env.sh

@@ -55,8 +55,7 @@ if pip list | grep -q ^pandas; then
 fi
 
 echo "Build extensions"
-# GH 47305: Parallel build can causes flaky ImportError from pandas/_libs/tslibs
-python setup.py build_ext -q -j1
+python setup.py build_ext -q -j4
 
 echo "Install pandas"
 python -m pip install --no-build-isolation --no-use-pep517 -e .

.github/workflows/32-bit-linux.yml

@@ -42,7 +42,7 @@ jobs:
           python -m pip install --no-deps -U pip wheel 'setuptools<60.0.0' && \
           python -m pip install versioneer[toml] && \
           python -m pip install cython numpy python-dateutil pytz pytest>=7.0.0 pytest-xdist>=2.2.0 pytest-asyncio>=0.17 hypothesis>=6.34.2 && \
-          python setup.py build_ext -q -j1 && \
+          python setup.py build_ext -q -j$(nproc) && \
           python -m pip install --no-build-isolation --no-use-pep517 -e . && \
           python -m pip list && \
           export PANDAS_CI=1 && \

.github/workflows/python-dev.yml

@@ -81,10 +81,9 @@ jobs:
         python -m pip install python-dateutil pytz cython hypothesis>=6.34.2 pytest>=7.0.0 pytest-xdist>=2.2.0 pytest-cov pytest-asyncio>=0.17
         python -m pip list
 
-    # GH 47305: Parallel build can cause flaky ImportError from pandas/_libs/tslibs
     - name: Build Pandas
       run: |
-        python setup.py build_ext -q -j1
+        python setup.py build_ext -q -j4
         python -m pip install -e . --no-build-isolation --no-use-pep517 --no-index
 
     - name: Build Version