ci: Tweaks to GitHub Actions setup

Remove some unnecessary package dependencies.  Also include testing of the
'ci' branch (so as to test in-progress changes to the CI configuration
itself).

Generated-by: Claude Code 1.0.65 (claude-sonnet-4@20250514)
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

.github/workflows/build.yml

@@ -4,6 +4,7 @@ name: Build test
   push:
     branches:
       - main
+      - ci
   pull_request:
     branches:
       - main

scripts/install-deps.sh

@@ -12,20 +12,20 @@ fi
 if [ "$NAME" = "Arch Linux" ]
 then
     pacman -Syu --needed --noconfirm bison diffutils flex gcc git libyaml \
-    make meson pkgconf python python-setuptools-scm swig valgrind which
+    make meson pkgconf python python-setuptools-scm swig
 elif [ "$NAME" = "Alpine Linux" ]
 then
-    apk add build-base bison coreutils flex git yaml yaml-dev python3-dev \
-    meson py3-setuptools_scm swig valgrind
+    apk add build-base bison flex git yaml yaml-dev python3-dev \
+    meson py3-setuptools_scm swig
 elif [ "$NAME" = "Fedora Linux" ]
 then
     dnf install -y bison diffutils flex gcc git libyaml libyaml-devel \
-    make meson python3-devel python3-setuptools swig valgrind which
+    make meson python3-devel python3-setuptools swig
 elif [ "$NAME" = "Ubuntu" ]
 then
     apt update
     apt install -yq build-essential bison flex git libyaml-dev pkg-config \
-    meson python3-dev python3-setuptools python3-setuptools-scm swig valgrind
+    meson python3-dev python3-setuptools python3-setuptools-scm swig
 else
     echo "ERROR: OS name is not provided."
     exit 1