Bump ffmpeg to 8.1.1 in manylinux2014 i686 build

The i686 build was the only architecture still pinning the old
ffmpeg 5.1.4 (libavcodec.so.59); every other arch/libc combination
(manylinux_2_28, manylinux2014 x86_64/aarch64, musllinux_1_2) already
builds ffmpeg 8.1.1. This aligns i686 with the rest and pulls in the
security fixes tracked in #1212 and #1228.

Verified: ffmpeg-8.1.1.tar.bz2 is published at the same release URL the
recipe uses, and all ffmpeg configure flags in this recipe
(--enable-openssl/libvpx/shared/pic) remain valid in 8.1.1. The i686
toolchain (NASM 2.15.04, OpenSSL 1.1.1w) matches the x86_64 recipe that
already ships 8.1.1, so build dependencies are unchanged.

Author: MDSALMANSHAMS

docker/manylinux2014/Dockerfile_i686

@@ -2,7 +2,7 @@ FROM quay.io/pypa/manylinux2014_i686:latest
 
 ARG CCACHE_VERSION=3.7.9
 ARG CMAKE_VERSION=3.17.0
-ARG FFMPEG_VERSION=5.1.4
+ARG FFMPEG_VERSION=8.1.1
 ARG NASM_VERSION=2.15.04
 ARG OPENSSL_VERSION=1_1_1w
 ARG QT_VERSION=5.15.0