d/tests: Use AUTOPKGTEST_TMP instead of ADTTMP

debian/changelog

@@ -1,10 +1,14 @@
 ostree (2018.8-2) UNRELEASED; urgency=medium
 
+  [ Simon McVittie ]
   * ostree-tests: Remove gjs dependency on s390x.
     mozjs60 doesn't work on s390x, so gjs is in danger of being removed
     from that architecture (see #909536). The test that uses JS is
     automatically skipped if the interpreter is missing.
 
+  [ Ondřej Nový ]
+  * d/tests: Use AUTOPKGTEST_TMP instead of ADTTMP
+
  -- Simon McVittie <smcv@debian.org>  Thu, 27 Sep 2018 19:45:55 +0100
 
 ostree (2018.8-1) unstable; urgency=medium

debian/tests/build

@@ -4,7 +4,7 @@ set -e
 exec 2>&1
 set -x
 
-cd "$ADTTMP"
+cd "$AUTOPKGTEST_TMP"
 
 cat > trivial.c <<EOF
 #include <ostree.h>