github: Disable building docs in ffmpeg

This avoids failing if building in an environment where texinfo
exists, but is a newer version. (Support for texinfo 7.1 and 7.2
was added in ffmpeg 8.0.)

Ubuntu 26.04 contains a version of texinfo that fails to build
the docs in ffmpeg 6.0.2. The "ubuntu-latest" runners on Github
Actions are now running on Ubuntu 26.04.

.github/workflows/build.yml

@@ -732,7 +732,7 @@ jobs:
           # Make sure we exit in a reasonable time instead of waiting for
           # the whole github actions timeout of 6h before exiting.
           ulimit -t 180
-          ../ffmpeg/configure --arch=${{matrix.arch}} --target-os=mingw32 --cross-prefix=${{matrix.arch}}-w64-mingw32- --enable-gpl
+          ../ffmpeg/configure --arch=${{matrix.arch}} --target-os=mingw32 --cross-prefix=${{matrix.arch}}-w64-mingw32- --enable-gpl --disable-doc
           make -j$(nproc)
 
   # Test building ffmpeg for natively on x86_64 Windows and run its tests,
@@ -781,7 +781,7 @@ jobs:
           export PATH=/llvm-mingw/bin:$PATH
           mkdir ffmpeg-build
           cd ffmpeg-build
-          ../ffmpeg/configure --samples=../fate-samples --enable-gpl
+          ../ffmpeg/configure --samples=../fate-samples --enable-gpl --disable-doc
           make -j$(nproc)
           make fate-rsync || make fate-rsync
           make -j$(nproc) fate