Use git-core pkg instead of git

[weyfonk]

Follow-up to #2098, refers to #2008.
Original PR submitted to rancher/gitjob by @macedogm, with the following description (verbatim):

Use the base level package git-core that has less dependencies than git, reducing image size and possibly future CVEs ("less packages normally means less CVEs").

git

/ # zypper in git
Refreshing service 'container-suseconnect-zypp'.
Loading repository data...
Reading installed packages...
Resolving package dependencies...

The following 12 NEW packages are going to be installed:
  file git git-core less libexpat1 libgdbm4 libpcre2-8-0 libsha1detectcoll1 perl perl-Error perl-Git which

The following 12 packages are not supported by their vendor:
  file git git-core less libexpat1 libgdbm4 libpcre2-8-0 libsha1detectcoll1 perl perl-Error perl-Git which

12 new packages to install.
Overall download size: 12.5 MiB. Already cached: 0 B. After the operation, additional 69.5 MiB will be used.

git-core

/ # zypper in git-core
Refreshing service 'container-suseconnect-zypp'.
Loading repository data...
Reading installed packages...
Resolving package dependencies...

The following 7 NEW packages are going to be installed:
  file git-core less libexpat1 libpcre2-8-0 libsha1detectcoll1 which

The following 7 packages are not supported by their vendor:
  file git-core less libexpat1 libpcre2-8-0 libsha1detectcoll1 which

7 new packages to install.
Overall download size: 5.6 MiB. Already cached: 0 B. After the operation, additional 28.5 MiB will be used.