apt: fix reproducibility issue

apt: fix reproducibility issue

In oe-selftest of reproducibility, recipe apt has reproducibility issue:

...
2025-09-20 17:09:18,986 - oe-selftest - INFO - ======================================================================
2025-09-20 17:09:18,986 - oe-selftest - INFO - FAIL: test_reproducible_builds (reproducible.ReproducibleTests)
2025-09-20 17:09:18,986 - oe-selftest - INFO - ----------------------------------------------------------------------
2025-09-20 17:09:18,986 - oe-selftest - INFO - Traceback (most recent call last):
  File "/buildarea5/hjia/contrib/openembedded-core-contrib/meta/lib/oeqa/selftest/cases/reproducible.py", line 406, in test_reproducible_builds
    self.fail('\n'.join(fails))
AssertionError: The following deb packages are different and not in exclusion list:
build-st/reproducibleB-extended/tmp/deploy/deb/./x86-64-v3/apt-dbg_3.0.3-r0_amd64.deb
build-st/reproducibleB-extended/tmp/deploy/deb/./x86-64-v3/apt_3.0.3-r0_amd64.deb
The following ipk packages are different and not in exclusion list:
build-st/reproducibleB-extended/tmp/deploy/ipk/./x86-64-v3/apt-dbg_3.0.3-r0_x86-64-v3.ipk
build-st/reproducibleB-extended/tmp/deploy/ipk/./x86-64-v3/apt_3.0.3-r0_x86-64-v3.ipk
The following rpm packages are different and not in exclusion list:
build-st/reproducibleB-extended/tmp/deploy/rpm/./x86_64_v3/apt-3.0.3-r0.x86_64_v3.rpm
build-st/reproducibleB-extended/tmp/deploy/rpm/./x86_64_v3/apt-dbg-3.0.3-r0.x86_64_v3.rpm
...

Due to upstream apt commit [1], it calls `id -gn root' in cmake
to set ROOT_GROUP if not define. The output of `id -gn root' may
differ in the compared builds which caused reproducibility issue
...
|build-st/reproducibleB-extended/tmp/work/x86-64-v3-oe-linux/apt/
3.0.3/temp/log.do_configure:124:-- Found root group: wheel
...
|build-st/reproducibleA/tmp/work/x86-64-v3-oe-linux/apt/3.0.3/
temp/log.do_configure:124:-- Found root group: root
...

Explicitly set ROOT_GROUP = "root" for cmake other than call `id -gn root'
to support reproducibility

[1] https://salsa.debian.org/apt-team/apt/-/commit/6f1f3c9afdb6ade6a7be110b90c8fc9e603254cf

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>