Ninja can compile test-fdb-feedback-theme.c before lfb-gdbus.h is generated

This leads to compile errors such as:

[1/49] Compiling C object 'tests/59830eb@@test-fbd-feedback-theme@exe/test-fbd-feedback-theme.c.o'.
ninja: job failed: gcc -Itests/59830eb@@test-fbd-feedback-theme@exe -Itests -I../tests -Isrc -I../src -Ilibfeedback -I../libfeedback -Idata -I../data -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/libmount -I/usr/include/blkid -I/usr/include/gio-unix-2.0 -I/usr/include/gudev-1.0 -I/usr/include/json-glib-1.0 -fdiagnostics-color=always -pipe -D_FILE_OFFSET_BITS=64 -std=gnu11 '-DFEEDBACKD_THEME_DIR="/usr/share/feedbackd/themes"' -DLIBFEEDBACK_COMPILATION -Wcast-align -Wdate-time -Werror=format-security -Werror=format=2 -Wendif-labels -Werror=incompatible-pointer-types -Werror=missing-declarations -Werror=overflow -Werror=return-type -Werror=shift-count-overflow -Werror=shift-overflow=2 -Werror=implicit-fallthrough=3 -Wformat-nonliteral -Wformat-security -Winit-self -Wmaybe-uninitialized -Wmissing-field-initializers -Wmissing-include-dirs -Wmissing-noreturn -Wnested-externs -Wno-missing-field-initializers -Wno-sign-compare -Wno-strict-aliasing -Wno-unused-parameter -Wold-style-definition -Wpointer-arith -Wredundant-decls -Wstrict-prototypes -Wtype-limits -Wundef -Wunused-function -Os -fomit-frame-pointer -Os -fomit-frame-pointer -fPIE -pthread '-DTEST_APP_ID="org.sigxcpu.feedbackd_test"' -MD -MQ 'tests/59830eb@@test-fbd-feedback-theme@exe/test-fbd-feedback-theme.c.o' -MF 'tests/59830eb@@test-fbd-feedback-theme@exe/test-fbd-feedback-theme.c.o.d' -o 'tests/59830eb@@test-fbd-feedback-theme@exe/test-fbd-feedback-theme.c.o' -c ../tests/test-fbd-feedback-theme.c
In file included from ../src/fbd-event.h:9,
                 from ../src/fbd-feedback-theme.h:8,
                 from ../tests/test-fbd-feedback-theme.c:8:
../src/fbd-feedback-manager.h:10:10: fatal error: lfb-gdbus.h: No such file or directory
   10 | #include "lfb-gdbus.h"
      |          ^~~~~~~~~~~~~
compilation terminated.
ninja: subcommand failed

Running: ninja data/lfb-gdbus.h fixes this, but instead a proper dependency should be formulated in the meson file.