Add support for Rocky Linux build automation

[jacksavage]

The Rocky Linux jobs in /.gitlab-ci.yml have been virtually disabled using when: manual. This means they will only be run if someone clicks a button from the pipeline view in the GitLab UI. As the support for Rocky Linux build automation stands, an error is encountered when trying to install GridPACK to the container environment after running /usr/bin/python3 setup.py build. This can be seen in job #165811 on GitLab.

Originally posted by @jacksavage in #195 (comment)

[wperkins]

At some point, CMake decided that case matters. This change solves this problem for me:

diff --git a/python/setup.py b/python/setup.py
index 0068efc8..90744ec9 100644
--- a/python/setup.py
+++ b/python/setup.py
@@ -40,6 +40,7 @@ class CMakeBuild(build_ext):
         extdir = os.path.abspath(os.path.dirname(self.get_ext_fullpath(ext.name)))
         cmake_args = ['-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=' + extdir,
                       '-DPYTHON_EXECUTABLE=' + sys.executable,
+                      '-DPython_EXECUTABLE=' + sys.executable,
                       '-DCMAKE_VERBOSE_MAKEFILE=YES' ]
 
         cfg = 'Debug' if self.debug else 'Release'