CI: Ubuntu install gcc-10

FFmpeg refuses to build on gcc 9, because of missing intrinsic
_mm256_loadu2_m128i

Author: mpiatka

.github/scripts/Linux/prepare.sh

@@ -28,6 +28,11 @@ sudo apt install libcurl4-nss-dev
 sudo apt install i965-va-driver-shaders # instead of i965-va-driver
 sudo apt install uuid-dev # Cineform
 
+sudo apt install gcc-10
+sudo apt install g++-10
+sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 10
+sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-10 10
+
 get_build_deps_excl() { # $2 - pattern to exclude
         apt-cache showsrc "$1" | sed -n '/^Build-Depends:/{s/Build-Depends://;p;q}' | tr ',' '\n' | cut -f 2 -d\  | grep -v "$2"
 }