CI: install libsqlite3-dev for find_package(SQLite3 REQUIRED)

PR #983 added a hard SQLite3 system dependency to CMakeLists.txt, but
the workflow only installed libqt6sql6-sqlite (Qt's runtime driver
plugin), not the C headers/library find_package(SQLite3) needs. Every
PR based on current master has been failing CI with "Could NOT find
SQLite3" since #983 merged.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/linux-build.yml

@@ -28,7 +28,7 @@ jobs:
           DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
             ca-certificates build-essential cmake ninja-build git pkg-config \
             qt6-base-dev qt6-base-private-dev qt6-tools-dev qt6-tools-dev-tools \
-            libqt6svg6-dev libqt6sql6-sqlite libcups2-dev \
+            libqt6svg6-dev libqt6sql6-sqlite libcups2-dev libsqlite3-dev \
             libxkbcommon-x11-0 \
             xvfb openbox xdotool x11-utils
           # extra-cmake-modules and the KF6 libraries are installed rather than