mkarchiso: use C.UTF-8

The glibc 2.35-6 package ships with the C.UTF-8 locale included, so mkarchiso does not need to use a non-UTF-8 locale anymore.

Implements #175.

CHANGELOG.rst

@@ -14,6 +14,8 @@ Changed
 -------
 
 - Change the releng profile's locale from ``en_US.UTF-8`` to ``C.UTF-8``.
+- Set ``LC_ALL`` to ``C.UTF-8`` instead of ``C`` in mkarchiso since it is now available and non-UTF-8 locales should be
+  avoided.
 
 Removed
 -------

archiso/mkarchiso

@@ -6,7 +6,7 @@ set -e -u
 
 # Control the environment
 umask 0022
-export LC_ALL="C"
+export LC_ALL="C.UTF-8"
 [[ -v SOURCE_DATE_EPOCH ]] || printf -v SOURCE_DATE_EPOCH '%(%s)T' -1
 export SOURCE_DATE_EPOCH