Update SyncThingy.yml to use new libportal source

[muelli]

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[muelli]

========================================================================
Building module libportal in /work/.flatpak-builder/build/libportal-1
========================================================================
FB: Running: flatpak build --die-with-parent --env=FLATPAK_BUILDER_BUILDDIR=/run/build/libportal --nofilesystem=host:reset --filesystem=/work/.flatpak-builder/build/libportal-1 --bind-mount=/run/build/libportal=/work/.flatpak-builder/build/libportal-1 --bind-mount=/run/active-build=/work/.flatpak-builder/build/libportal-1 --build-dir=/run/build/libportal/_flatpak_build --bind-mount=/run/ccache=/work/.flatpak-builder/ccache --unshare=network --env=SOURCE_DATE_EPOCH=1321009871 '--env=CFLAGS=-O2 -pipe -g -Wp,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -fasynchronous-unwind-tables -fstack-clash-protection -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -mbranch-protection=bti+pac-ret ' '--env=CXXFLAGS=-O2 -pipe -g -Wp,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -fasynchronous-unwind-tables -fstack-clash-protection -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -mbranch-protection=bti+pac-ret ' '--env=LDFLAGS=-L/app/lib -Wl,-z,relro,-z,now -Wl,--as-needed ' --env=CCACHE_DIR=/run/ccache --env=PATH=/run/ccache/bin:/app/bin:/usr/bin --env=LD_LIBRARY_PATH=/app/lib --env=PKG_CONFIG_PATH=/app/lib/pkgconfig:/app/share/pkgconfig:/usr/lib/pkgconfig:/usr/share/pkgconfig --env=FLATPAK_BUILDER_N_JOBS=8 /work/builddir meson setup --wrap-mode=nodownload --prefix=/app --libdir=/app/lib .. -Dbackends=qt5 -Dintrospection=false -Ddocs=false
The Meson build system
Version: 1.9.1
Source dir: /run/build/libportal
Build dir: /run/build/libportal/_flatpak_build
Build type: native build

../meson.build:1:0: ERROR: Unknown option: "backends".

A full log can be found at /run/build/libportal/_flatpak_build/meson-logs/meson-log.txt
Error: module libportal: Child process exited with code 1
error: Recipe `build` failed with exit code 1