ext/svt.sh: Do not build the SVT-AV1 decoder

src/codec_svt.c only supports using SVT-AV1 as an AV1 encoder.

Temporarily turn off caching for the "Build SVT-AV1" step in
.github/workflows/ci.yml, otherwise SVT-AV1 does not seem to be rebuilt
in the ubuntu-latest os image.
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e601f94..87f4eed 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -47,7 +47,7 @@
       working-directory: ./ext
       run: bash rav1e.cmd
     - name: Build SVT-AV1
-      if: steps.cache-ext.outputs.cache-hit != 'true'
+      #if: steps.cache-ext.outputs.cache-hit != 'true'
       working-directory: ./ext
       run: bash svt.cmd
     - name: Build libgav1
diff --git a/ext/svt.sh b/ext/svt.sh
index b01f62f..6b22b92 100644
--- a/ext/svt.sh
+++ b/ext/svt.sh
@@ -7,7 +7,7 @@
 cd SVT-AV1
 cd Build/linux
 
-./build.sh release static
+./build.sh release static no-dec
 cd ../..
 mkdir -p include/svt-av1
 cp Source/API/*.h include/svt-av1