‘frame_number’ is deprecated

[CRAG666]

@jbuchermn Hi, sorry to bother you, I know you're very busy lately, I hope you're well. First of all thanks for this amazing project. When trying to build it throws the following error

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ninja: Entering directory `build'
[1/2] Compiling C object subprojects/wlroots/examples/dmabuf-capture.p/dmabuf-capture.c.o
FAILED: subprojects/wlroots/examples/dmabuf-capture.p/dmabuf-capture.c.o
cc -Isubprojects/wlroots/examples/dmabuf-capture.p -Isubprojects/wlroots/examples -I../subprojects/wlroots/examples -Isubprojects/wlroots/protocol -I/usr/include/libdrm -fdiagnostics-color=always - D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=c11 -O0 -g -DWLR_USE_UNSTABLE -DWLR_LITTLE_ENDIAN=1 -DWLR_BIG_ENDIAN=0 -Wundef -Wlogical-op -Wmissing-include-dirs -Wold-style-definition - Wpointer-arith -Winit-self -Wstrict-prototypes -Wimplicit-fallthrough=2 -Wendif-labels -Wstrict-aliasing=2 -Woverflow -Wmissing-prototypes -Walloca -Wno-missing-braces -Wno-missing-field-initializers - Wno-unused-parameter -fmacro-prefix-map=../subprojects/wlroots/= -DHAS_GBM_BO_GET_FD_FOR_PLANE=1 -DLIBINPUT_HAS_HOLD_GESTURES=1 '-DICONDIR="/usr/local/share/icons"' -DHAS_XCB_ERRORS=1 -pthread - MD -MQ subprojects/wlroots/examples/dmabuf-capture.p/dmabuf-capture.c.o -MF subprojects/wlroots/examples/dmabuf-capture.p/dmabuf-capture.c.o.d -o subprojects/wlroots/examples/dmabuf-capture .p/dmabuf-capture.c.o -c ../subprojects/wlroots/examples/dmabuf-capture.c
../subprojects/wlroots/examples/dmabuf-capture.c: In the function 'vid_encode_thread':
../subprojects/wlroots/examples/dmabuf-capture.c:524:33: error: 'frame_number' is deprecated [-Werror=deprecated-declarations]
   524 | ctx->avctx->frame_number, get_fifo_size(&ctx->vid_frames));
       | ^~~
In the included file from ../subprojects/wlroots/examples/dmabuf-capture.c:2:
/usr/include/libavcodec/avcodec.h:1076:9: note: declared here
  1076 | int frame_number;
       | ^~~~~~~~~~~~
cc1: all warnings are treated as errors
ninja: build stopped: subcommand failed.