build-unit-test-docker: Also install abi-dumper

It turns out `abi-dumper` is not a dependency of
`abi-compliance-checker`, so we must install both.

Change-Id: I37547f87106cb738d155e53108e581c0e13958f3
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 5539085..0c71b1e 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -752,6 +752,7 @@
 
 RUN apt-get update && apt-get dist-upgrade -yy && apt-get install -yy \
     abi-compliance-checker \
+    abi-dumper \
     autoconf \
     autoconf-archive \
     bison \