tests: Avoid accidental matching of the vendor field of $host, part 2

* tests/local.mk (TESTS_ENVIRONMENT): Remove host_triplet.
* tests/chgrp/basic.sh: Use $host_os instead of $host_triplet.
* tests/misc/io-errors.sh: Likewise.

tests/chgrp/basic.sh

@@ -102,7 +102,7 @@ test "$(ls -C -c -t f g)" = 'f  g' || \
       openbsd*) echo ignoring known OpenBSD-specific chgrp failure 1>&2 ;;
       darwin7.9.*|darwin8.*)
         echo ignoring known MacOS X-specific chgrp failure 1>&2 ;;
-      *) echo $host_triplet: no-change chgrp failed to update ctime 1>&2;
+      *) echo $host_os: no-change chgrp failed to update ctime 1>&2;
             fail=1 ;;
     esac
   }

tests/local.mk

@@ -68,7 +68,6 @@ TESTS_ENVIRONMENT =				\
   built_programs='$(built_programs) $(single_binary_progs)' \
   fail=0					\
   host_os=$(host_os)				\
-  host_triplet='$(host_triplet)'		\
   srcdir='$(srcdir)'				\
   top_srcdir='$(top_srcdir)'			\
   CONFIG_HEADER='$(abs_top_builddir)/$(CONFIG_INCLUDE)' \

tests/misc/io-errors.sh

@@ -88,7 +88,7 @@ while read writer; do
   # As a result, when we print a single line there is no bytes buffered when
   # we close the stream and errno is not set.  See:
   # <https://www.openwall.com/lists/musl/2026/04/02/1>.
-  case $host_triplet in
+  case $host_os in
     *-musl*) error_re="$error_re|" ;;
   esac