[fenix] Issue https://github.com/mozilla-mobile/fenix/issues/21184: Update artifacts format

taskcluster/ci/toolchain/gecko-derived.yml

@@ -11,7 +11,7 @@ job-defaults:
 
 browsertime:
     attributes:
-        toolchain-artifact: public/build/browsertime.tar.bz2
+        toolchain-artifact: public/build/browsertime.tar.zst
     description: "Browsertime toolchain"
     run:
         index-search:
@@ -35,7 +35,7 @@ linux64-geckodriver:
 
 linux64-minidump-stackwalk:
     attributes:
-        toolchain-artifact: public/build/minidump_stackwalk.tar.xz
+        toolchain-artifact: public/build/minidump_stackwalk.tar.zst
     description: "minidump-stackwalk toolchain"
     run:
         index-search: