restoring no-build-isolation

Author: maureeungaro

ci/install_python_env.py

@@ -29,6 +29,8 @@
 subprocess.run([sys.executable, '-m', 'venv', str(venv_dir)], check=True)
 
 venv_python = str(venv_dir / 'bin' / 'python3')
-subprocess.run([venv_python, '-m', 'pip', 'install', '--no-cache-dir', '--upgrade',
-                'pip', 'setuptools', 'wheel'], check=True)
-subprocess.run([venv_python, '-m', 'pip', 'install', '--no-cache-dir', pygemc_src], check=True)
+subprocess.run([venv_python, '-m', 'pip', 'install', '--no-cache-dir',
+                '--upgrade', 'pip', 'setuptools'], check=True)
+# --no-build-isolation avoids pip spawning an extra isolated build env, reducing memory pressure.
+subprocess.run([venv_python, '-m', 'pip', 'install', '--no-cache-dir',
+                '--no-build-isolation', pygemc_src], check=True)