Revert "CI: parallel build follow up" (#51984)

Revert "CI: parallel build follow up (#51911)" This reverts commit 2c996a6.

Author: phofl

.github/actions/build_pandas/action.yml

@@ -16,5 +16,7 @@ runs:
  python -m pip install -e . --no-build-isolation --no-use-pep517 --no-index
  shell: bash -el {0}
  env:
- # https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners#supported-runners-and-hardware-resources
- N_JOBS: ${{ runner.os == 'macOS' && 3 || 2 }}
+ # Cannot use parallel compilation on Windows, see https://github.com/pandas-dev/pandas/issues/30873
+ # GH 47305: Parallel build causes flaky ImportError: /home/runner/work/pandas/pandas/pandas/_libs/tslibs/timestamps.cpython-38-x86_64-linux-gnu.so: undefined symbol: pandas_datetime_to_datetimestruct
+ N_JOBS: 1
+ #N_JOBS: ${{ runner.os == 'Windows' && 1 || 2 }}

.github/actions/setup-conda/action.yml

@@ -30,7 +30,7 @@ runs:
  environment-name: ${{ inputs.environment-name }}
  extra-specs: ${{ inputs.extra-specs }}
  channels: conda-forge
- channel-priority: 'strict'
+ channel-priority: ${{ runner.os == 'macOS' && 'flexible' || 'strict' }}
  condarc-file: ci/condarc.yml
  cache-env: true
  cache-downloads: true