Fix python

fuchsia-vendored-python is the correct place to find the python
interpreter.

Change-Id: Icff5310eff48eb3ab26705473bab43418b6812f9
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/vulkan-cts/+/729293
Reviewed-by: Craig Stout <cstout@google.com>
diff --git a/fuchsia/build.sh b/fuchsia/build.sh
index cc3194e..3bfbfbf 100755
--- a/fuchsia/build.sh
+++ b/fuchsia/build.sh
@@ -41,7 +41,7 @@
 export PATH="$PATH:$(dirname $cmake)"
 
 pushd $fuchsia_root/third_party/vulkan-cts
-python3.8 external/fetch_sources.py
+$fuchsia_root/scripts/fuchsia-vendored-python external/fetch_sources.py
 popd
 
 mkdir -p $build_dir