qemu-build: Install python3-tomli

At least at v9.1.0 qemu depends on python3-tomli. Install it so we can
build.

Change-Id: I9d2f938944515c45dc72f85f37acebd71b59576d
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/qemu-build.sh b/qemu-build.sh
index b2d0224..a00947d 100755
--- a/qemu-build.sh
+++ b/qemu-build.sh
@@ -127,6 +127,7 @@
     libslirp-dev \
     make \
     ninja-build \
+    python3-tomli \
     python3-venv \
     python3-yaml \
     iputils-ping