[REQ] Update `git_push.sh` to Comply With Basic ShellCheck

[georglauterbach]

Is your feature request related to a problem? Please describe.

I want to update git_push.sh.mustache so that it complies with basic ShellCheck.

Describe the solution you'd like

The following issues can be fixed easily and without being invasive:

1. SC2250: Prefer putting braces around variable references even when not strictly required
2. SC2086: Double quote to prevent globbing and word splitting
3. SC2154: var is referenced but not assigned

I would be implementing these changes. It mostly boils down to adding braces and adding quotes.

Describe alternatives you've considered

N/A

Additional context

Having the scripts compliant with basic shellcheck is quite important because users of this projects will have their linting pipelines fail without an easy way of fixing it (as it is an upstream issue9. I highly urge maintainers to approve of this change and let me fix this :)

[wing328]

sounds good

please open a PR and we will try to get it merged before the upcoming stable release.

[georglauterbach]

@wing328 I opened #24689, but I am not 100% I ran all scripts properly. ./mvnw clean package did not succeed for me.