meson: Fix failing libva wrap file build

Review request: @nirbheek

gst-plugins-bad| Dependency libva found: NO found 1.7.0 but need: '>= 1.12'
gst-plugins-bad| Run-time dependency libva found: NO (tried pkgconfig and cmake)
gst-plugins-bad| Looking for a fallback subproject for the dependency libva
gst-plugins-bad| Downloading libva source from https://github.com/intel/libva/releases/download/2.21.0/libva-2.21.0.tar.bz2
Download size: 521730
Downloading: ..........

Executing subproject gst-plugins-bad:libva

libva| Project name: libva
libva| Project version: 2.21.0
libva| C compiler for the host machine: cc (gcc 9.4.0 "cc (Ubuntu 9.4.0-1ubuntu1~20.04.2) 9.4.0")
libva| C linker for the host machine: cc ld.bfd 2.34
libva| Library dl found: YES
libva| Dependency libdrm found: YES 2.4.107 (cached)
libva| Dependency x11 found: YES 1.7.2 (cached)
libva| Dependency xext found: YES 1.3.4 (cached)
libva| Dependency xfixes found: YES 6.0.0 (cached)
libva| Dependency x11-xcb found: YES 1.7.2 (cached)
libva| Run-time dependency xcb found: YES 1.14
libva| Run-time dependency xcb-dri3 found: YES 1.14
libva| Run-time dependency gl found: YES 1.2
libva| Dependency wayland-client found: YES 1.18.0 (cached)
libva| Build-time dependency wayland-scanner found: YES 1.18.0
libva| Program /usr/bin/wayland-scanner found: YES (/usr/bin/wayland-scanner)
libva| Checking for function "secure_getenv" : YES
libva| Configuring va_version.h using configuration
libva| Checking if "-Wl,--version-script" : links: YES
libva| Program doxygen found: NO
libva| subprojects/libva-2.21.0/meson.build:161: WARNING: Project targets '>= 0.53.0' but uses feature introduced in '0.58.0': Calling "add_dist_script" in a subproject.

subprojects/libva-2.21.0/meson.build:161:6: ERROR: Program './autogen.sh' not found or not executable

A full log can be found at /tmp/gstreamer/gstreamer/builddir/meson-logs/meson-log.txt

The original libva.wrap file complained of a missing './autogen.sh' file, which was indeed missing in libva-2.21.0.tar.bz2 (https://github.com/intel/libva/releases/download/2.21.0/libva-2.21.0.tar.bz2).

Change to the automatically generated GitHub tag archive libva-2.21.0.tar.gz (https://github.com/intel/libva/archive/2.21.0.tar.gz) makes the build work again.