tests: use "env" to run commands with temporary env-var settings

diff --git a/RelNotes b/RelNotes
index 509b3f6044d1f0f5091c8e65826747d524ab12d0..bb52cf9476df53ddb9788f16082e2e92e76a4db5 120000 (symlink)
--- a/RelNotes
+++ b/RelNotes
@@ -1 +1 @@
-Documentation/RelNotes-1.5.3.7.txt
\ No newline at end of file
+Documentation/RelNotes/1.9.0.txt
\ No newline at end of file