filter-pixfmts-scale test fails when --enable-swscale but --disable-swscale-alpha

[Atemu]

Repro: Try to build ffmpeg with --enable-swscale and --disable-swscale-alpha.

I'm not sure why you'd want to do that but the options do exist, so they should work.

Additionally, swscale-alpha does not appear in the build configuration overview which made it unnecessarily hard to diagnose this issue.
I stumbled upon this issue while trying to refactor Nixpkgs ffmpeg build.

Error output for googlability:

--- ./tests/ref/fate/filter-pixfmts-scale       2022-04-14 20:13:38.000000000 +0000
+++ tests/data/fate/filter-pixfmts-scale        2022-12-09 12:17:13.038344819 +0000
@@ -19,9 +19,9 @@
 bgra64be            4e6a1b9f9c18b881c27d76611d45f737
 bgra64le            efeee0abcc658ebcff049d5e74d74943
 gbrap               4a100f750ac846b34bfeef0d6893c3de
-gbrap10be           dc6aea3559ea4fcdda1ccc4f23d2f2fb
+gbrap10be           50735fbc471a5ac5a6645c85881f3670
 gbrap10le           6e1cba57029fdf0f9d46b5e5cd55112b
-gbrap12be           dbe3a662c016563529032cd4dfb80262
+gbrap12be           58170165829484b3db4a3b9165198987
 gbrap12le           24f5ecb32435b73353517e017c165e31
 gbrap16be           31968e6872a46e8174fb57f8920ed10d
 gbrap16le           8c6758f33671b673b6d30969fc05a23d
TEST    vsynth2-dv-hd
TEST    vsynth2-dv-fhd
Test filter-pixfmts-scale failed. Look at tests/data/fate/filter-pixfmts-scale.err for details.
make: *** [tests/Makefile:256: fate-filter-pixfmts-scale] Error 1
make: *** Waiting for unfinished jobs....

(Version is actually 4.4.2 but that's not in the list; we're in the process of upgrading.)

[Carl Eugen Hoyos]

Please test current FFmpeg git head to make this a valid ticket.

[Atemu]

After removing the (apparently removed?) avresample enable flag, this does not happen with 7e8b5393895f6a21df501b047e5f987f456b9701 nor 4.4.3.