Update DIB to version 3.20.2

This newer version of DIB brings better btrfs support, containerfile
improvements, https ubuntu image downloads and RHEL/CentOS 9 EPEL
support.

Change-Id: I164cbfa7b71641288e880119b92515c505dafed3

requirements.txt

@@ -11,7 +11,7 @@ PrettyTable>=0.6,<0.8
 # 0.31.1 and 0.31.2 have a bug with image deletion in tasks API
 # We expect 1.0.0 to break the API we use
 openstacksdk>=0.27.0,!=0.28.0,!=0.29.0,!=0.30.0,!=0.31.0,!=0.31.1,!=0.31.2,<1.0.0
-diskimage-builder>=3.19.1
+diskimage-builder>=3.20.2
 voluptuous
 kazoo>=2.8.0
 Paste