test: do not hardcode /bin/true in the harness

OpenBSD has true(1) in /usr/bin, so EDITOR=/bin/true and OPENER=/bin/true
made mw -r fail with '/bin/true: not found'. Resolve true through PATH.

Author: daviduhden

tests/run_tests.sh

@@ -413,7 +413,8 @@ H10=$(mkhome "$TMP/h10")
 mw "$H10" -a one@example.com -f -x p -i i1.example.com -s s1.example.com >/dev/null 2>&1
 mw "$H10" -a two@example.com -f -x p -i i2.example.com -s s2.example.com >/dev/null 2>&1
 mkdir -p "$TMP/mwtmp"
-EDITOR=/bin/true TMPDIR="$TMP/mwtmp" expect "mw -r reorders accounts" mw "$H10" -r
+# `true` is resolved through PATH: /bin/true does not exist on OpenBSD.
+EDITOR=true TMPDIR="$TMP/mwtmp" expect "mw -r reorders accounts" mw "$H10" -r
 expect_file "muttrc regenerated with i1 macro" "$H10/.config/mutt/muttrc" 'macro index,pager i1'
 expect_file "muttrc regenerated with i2 macro" "$H10/.config/mutt/muttrc" 'macro index,pager i2'
 expect_file "default account sourced first" "$H10/.config/mutt/muttrc" "source $H10/.config/mutt/accounts/one@example.com.muttrc"
@@ -519,7 +520,7 @@ while [ "$(wc -l <"$OPENED_LOG" 2>/dev/null || echo 0)" -lt 2 ] && [ "$i" -lt 10
 done
 expect_file "macOS open recorded" "$OPENED_LOG" 'attach file.txt'
 
-OPENER=/bin/true expect 'openfile honors $OPENER' \
+OPENER=true expect 'openfile honors $OPENER' \
 	openfile "$H15" "$TMP/attach file.txt"
 
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