Update install.sh script to use longer template name

[ProbstenHias]

Using the install.sh script fails on alpine distributions as the installed mktemp tool on alpine expects at least 6 X when creating a temp folder with a template.

According to the tool installed on alpine

ecc23e77fdf2:/# mktemp --help
BusyBox v1.36.1 (2023-11-07 18:53:09 UTC) multi-call binary.

Usage: mktemp [-dt] [-p DIR] [TEMPLATE]

Create a temporary file with name based on TEMPLATE and print its name.
TEMPLATE must end with XXXXXX (e.g. [/dir/]nameXXXXXX).
Without TEMPLATE, -t tmp.XXXXXX is assumed.
...

For that reason the install script fails on alpine with the error

mktemp: Invalid argument

This PR fixes the issue by adding two more x 😀

Fixes #767

[oracle-contributor-agreement]

Thank you for your pull request and welcome to our community! To contribute, please sign the Oracle Contributor Agreement (OCA).
The following contributors of this PR have not signed the OCA:

• PR author: ProbstenHias
• matthias.weilinger@gmx.de (@ProbstenHias)

To sign the OCA, please create an Oracle account and sign the OCA in Oracle's Contributor Agreement Application.

When signing the OCA, please provide your GitHub username. After signing the OCA and getting an OCA approval from Oracle, this PR will be automatically updated.

If you are an Oracle employee, please make sure that you are a member of the main Oracle GitHub organization, and your membership in this organization is public.

[ProbstenHias]

Agreement is under review 👍🏻

[oracle-contributor-agreement]

Thank you for signing the OCA.