Auto merge of #21420 - gootorov:gstreamer-gentoo, r=jdm

Add needed gstreamer packages for Gentoo build

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r? @jdm

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #21418
- [x] These changes do not require tests because: docs

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README.md

@@ -146,7 +146,8 @@ sudo emerge net-misc/curl \
     media-libs/freetype media-libs/mesa dev-util/gperf \
     dev-python/virtualenv dev-python/pip dev-libs/openssl \
     media-libs/harfbuzz dev-util/ccache \
-    x11-libs/libXmu media-libs/glu x11-base/xorg-server sys-devel/clang
+    x11-libs/libXmu media-libs/glu x11-base/xorg-server sys-devel/clang \
+    media-libs/gstreamer media-libs/gst-plugins-bad media-libs/gst-plugins-base
 ```
 
 with the following environment variable set: