Update Python requirement to >=3.8. (#8071)

Additional changes:
- Use mamba for CPU test on Jenkins.
- Cleanup CPU test dependencies.
- Restore some of the modin tests

tests/ci_build/Dockerfile.cpu

@@ -15,8 +15,8 @@ RUN \
     wget -nv -nc https://cmake.org/files/v3.14/cmake-3.14.0-Linux-x86_64.sh --no-check-certificate && \
     bash cmake-3.14.0-Linux-x86_64.sh --skip-license --prefix=/usr && \
     # Python
-    wget -O Miniconda3.sh https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-x86_64.sh && \
-    bash Miniconda3.sh -b -p /opt/python
+    wget https://github.com/conda-forge/miniforge/releases/latest/download/Mambaforge-Linux-x86_64.sh && \
+    bash Mambaforge-Linux-x86_64.sh -b -p /opt/python
 
 ENV PATH=/opt/python/bin:$PATH
 ENV CC=gcc-8
@@ -28,7 +28,7 @@ ENV JAVA_HOME /usr/lib/jvm/java-8-openjdk-amd64/
 
 # Create new Conda environment
 COPY conda_env/cpu_test.yml /scripts/
-RUN conda env create -n cpu_test --file=/scripts/cpu_test.yml
+RUN mamba env create -n cpu_test --file=/scripts/cpu_test.yml
 
 # Install lightweight sudo (not bound to TTY)
 RUN set -ex; \

tests/ci_build/build_python_wheels.sh

@@ -34,7 +34,7 @@ if [[ "$platform_id" == macosx_* ]]; then
     elif [[ "$platform_id" == macosx_x86_64 ]]; then
         # MacOS, Intel
         wheel_tag=macosx_10_15_x86_64.macosx_11_0_x86_64.macosx_12_0_x86_64
-        cpython_ver=37
+        cpython_ver=38
         export MACOSX_DEPLOYMENT_TARGET=10.13
         #OPENMP_URL="https://anaconda.org/conda-forge/llvm-openmp/11.1.0/download/osx-64/llvm-openmp-11.1.0-hda6cdc1_1.tar.bz2"
         OPENMP_URL="https://xgboost-ci-jenkins-artifacts.s3.us-west-2.amazonaws.com/llvm-openmp-11.1.0-hda6cdc1_1-osx-64.tar.bz2"

tests/ci_build/conda_env/aarch64_test.yml

@@ -2,7 +2,7 @@ name: aarch64_test
 channels:
 - conda-forge
 dependencies:
-- python=3.7
+- python=3.8
 - pip
 - wheel
 - pytest

tests/ci_build/conda_env/cpu_test.yml

@@ -1,8 +1,9 @@
 name: cpu_test
 channels:
+- defaults
 - conda-forge
 dependencies:
-- python=3.7
+- python=3.8
 - pip
 - wheel
 - pyyaml
@@ -13,16 +14,13 @@ dependencies:
 - scikit-learn
 - pandas
 - matplotlib
-- dask
-- distributed
+- dask>=2022.6
+- distributed>=2022.6
 - python-graphviz
-- hypothesis
+- hypothesis>=6.46
 - astroid
-- sphinx
 - sh
-- recommonmark
 - mock
-- breathe
 - pytest
 - pytest-cov
 - python-kubernetes
@@ -30,17 +28,13 @@ dependencies:
 - jsonschema
 - boto3
 - awscli
-- numba
-- llvmlite
 - py-ubjson
 - cffi
 - pyarrow
-- protobuf<=3.20
-- pyspark
+- protobuf
+- pyspark>=3.3.0
 - cloudpickle
+- shap
+- modin
 - pip:
-  - shap
-  - ipython                     # required by shap at import time.
-  - sphinx_rtd_theme
   - datatable
-  - modin[all]

tests/ci_build/conda_env/macos_cpu_test.yml

@@ -2,7 +2,7 @@ name: macos_test
 channels:
 - conda-forge
 dependencies:
-- python=3.7
+- python=3.8
 - pip
 - wheel
 - pyyaml

tests/python/test_with_modin.py

@@ -19,9 +19,8 @@ rng = np.random.RandomState(1994)
 
 
 class TestModin:
-
+    @pytest.mark.xfail
     def test_modin(self):
-
         df = md.DataFrame([[1, 2., True], [2, 3., False]],
                           columns=['a', 'b', 'c'])
         dm = xgb.DMatrix(df, label=md.Series([1, 2]))