ci: add `fpart` package to apt dependencies

We need this for access to the `fpsync` tool, which we want to use to do
parallel copies from network drives backed by AWS ElasticFS.

Signed-off-by: Chris Kay <chris.kay@arm.com>
Change-Id: I679cd530aa2c9a4055f49208a69697c042bcd640
diff --git a/jammy-amd64-tf-a-build/Dockerfile b/jammy-amd64-tf-a-build/Dockerfile
index 0f5581e..63e28f2 100644
--- a/jammy-amd64-tf-a-build/Dockerfile
+++ b/jammy-amd64-tf-a-build/Dockerfile
@@ -22,6 +22,7 @@
     exuberant-ctags \
     file \
     flex \
+    fpart \
     g++-multilib \
     gcc-multilib \
     gdisk \