[BUG] It's not possible to list targets if "SYSROOT_AARCH64" is not defined

[arkq]

Reproduction steps

1. unset SYSROOT_AARCH64 (if defined)
2. ./scripts/build/build_examples.py targets
...
  File "/home/a.bokowy/connectedhomeip/scripts/build/build/targets.py", line 76, in Create
    builder = self.builder_class(
  File "/home/a.bokowy/connectedhomeip/scripts/build/builders/host.py", line 230, in __init__
    self.build_env['PKG_CONFIG_PATH'] = os.path.join(self.SysRootPath('SYSROOT_AARCH64'), 'lib/aarch64-linux-gnu/pkgconfig')
  File "/home/a.bokowy/connectedhomeip/scripts/build/builders/host.py", line 355, in SysRootPath
    raise Exception('Missing environment variable "%s"' % name)
Exception: Missing environment variable "SYSROOT_AARCH64"

Bug prevalence

always

GitHub hash of the SDK that was being used

n/a

Platform

core

Platform Version(s)

No response

Anything else?

No response