Revert "Bump ASDF version to 0.16.0"

Author: dduportal

provisioning/tools-versions.yml

@@ -1,5 +1,5 @@
 # if manually change, please update the goss file accordingly
-asdf_version: 0.16.0
+asdf_version: 0.15.0
 awscli_version: 2.23.9
 azcopy_version: 10.28.0
 azurecli_version: 2.68.0

tests/goss-linux.yaml

@@ -5,7 +5,7 @@ command:
     exec: asdf version
     exit-status: 0
     stdout:
-      - v0.16.0
+      - v0.15.0
   azcopy:
     exec: azcopy --version
     exit-status: 0