CI: Disable PipeWire on Ubuntu

Unfortunately, neither Ubuntu 20.04 nor 18.04 have a recent enough
PipeWire package. Disable the PipeWire bits of linux-capture there.
The Flatpak workflow is still able to build it, so keep it enabled
there.

.github/workflows/main.yml

@@ -444,7 +444,7 @@ jobs:
         run: |
           mkdir ./build
           cd ./build
-          cmake -DUNIX_STRUCTURE=0 -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/obs-studio-portable" -DENABLE_UNIT_TESTS=ON -DENABLE_VLC=ON -DWITH_RTMPS=ON -DBUILD_BROWSER=ON -DCEF_ROOT_DIR="${{ github.workspace }}/cmbuild/cef_binary_${{ env.LINUX_CEF_BUILD_VERSION }}_linux64" -DTWITCH_CLIENTID='${{ env.TWITCH_CLIENTID }}' -DTWITCH_HASH='${{ env.TWITCH_HASH }}' -DRESTREAM_CLIENTID='${{ env.RESTREAM_CLIENTID }}' -DRESTREAM_HASH='${{ env.RESTREAM_HASH }}' ..
+          cmake -DENABLE_PIPEWIRE=OFF -DUNIX_STRUCTURE=0 -DCMAKE_INSTALL_PREFIX="${{ github.workspace }}/obs-studio-portable" -DENABLE_UNIT_TESTS=ON -DENABLE_VLC=ON -DWITH_RTMPS=ON -DBUILD_BROWSER=ON -DCEF_ROOT_DIR="${{ github.workspace }}/cmbuild/cef_binary_${{ env.LINUX_CEF_BUILD_VERSION }}_linux64" -DTWITCH_CLIENTID='${{ env.TWITCH_CLIENTID }}' -DTWITCH_HASH='${{ env.TWITCH_HASH }}' -DRESTREAM_CLIENTID='${{ env.RESTREAM_CLIENTID }}' -DRESTREAM_HASH='${{ env.RESTREAM_HASH }}' ..
       - name: 'Build'
         shell: bash
         working-directory: ${{ github.workspace }}/build

CI/before-script-linux.sh

@@ -3,4 +3,4 @@
 set -ex
 ccache -s || echo "CCache is not available."
 mkdir build && cd build
-cmake -DBUILD_BROWSER=ON -DCEF_ROOT_DIR="../cef_binary_${LINUX_CEF_BUILD_VERSION}_linux64" ..
+cmake -DENABLE_PIPEWIRE=OFF -DBUILD_BROWSER=ON -DCEF_ROOT_DIR="../cef_binary_${LINUX_CEF_BUILD_VERSION}_linux64" ..