Fix nightly container testing suite (#495)

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## Description

Changing container user to root requires changes to how pip and pytest
work, so needed update for this.

closes #494 

## Issue
closes #494

## Checklist

- [x] I am familiar with the [Contributing
Guidelines](https://github.com/NVIDIA/cuopt/blob/HEAD/CONTRIBUTING.md).
- Testing
   - [ ] New or existing tests cover these changes
   - [ ] Added tests
   - [ ] Created an issue to follow-up
   - [x] NA
- Documentation
   - [ ] The documentation is up to date with these changes
   - [ ] Added new documentation
   - [x] NA

Author: rgsl888prabhu

ci/docker/test_image.sh

@@ -19,7 +19,7 @@ set -euo pipefail
 
 # Install dependencies
 apt-get update
-DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends file bzip2
+DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends file bzip2 gcc
 
 # Download test data
 bash datasets/linear_programming/download_pdlp_test_dataset.sh
@@ -37,7 +37,7 @@ chmod -R a+w "$(pwd)"
 
 cat > /opt/cuopt/test.sh <<EOF
 cd /opt/cuopt/cuopt
-pip install pytest pexpect
+python -m pip install pytest pexpect
 export RAPIDS_DATASET_ROOT_DIR=\$(realpath datasets)
 echo '----------------- CLI TEST START ---------------'
 bash python/libcuopt/libcuopt/tests/test_cli.sh