GITHUB_HOSTNAME is ignored

**Describe the bug**
I exported my GHE host as:
export GITHUB_HOSTNAME="github.houston.softwaregrp.net"

When I run git-xargs it seems to be trying to clone from github.com:
[git-xargs] INFO[2024-01-29T17:40:17-05:00] git-xargs running...
[git-xargs] DEBU[2024-01-29T17:40:17-05:00] Looking up filename provided repo Name=beanutils Organization=identity-governance-team
[git-xargs] DEBU[2024-01-29T17:40:17-05:00] error getting single repo AllowedRepoName=beanutils AllowedRepoOwner=identity-governance-team Error="GET https://**api.github.com**/repos/identity-governance-team/beanutils: 401 Bad credentials []" Response Status Code=401
ERROR: GET https://api.github.com/repos/identity-governance-team/beanutils: 401 Bad credentials []

**To Reproduce**
Steps to reproduce the behavior including the relevant Terraform/Terragrunt/Packer version number and any code snippets and module inputs you used.

```shell
export GITHUB_HOSTNAME="github.houston.softwaregrp.net"
export LOG_LEVEL=TRACE

git-xargs \
--repos /tmp/xargs-repos.txt \
--branch-name parentpomupdate \
--commit-message "Updated parent pom version" \
--loglevel "${LOG_LEVEL}" \
--keep-cloned-repositories true \
--dry-run \
update-parent-pom-version.sh pom.xml "${version}"
```

**Expected behavior**
The clone command should be against my specified GHE server.

[xargs-repos.txt](https://github.com/gruntwork-io/git-xargs/files/14187026/xargs-repos.txt)