devops(firefox): fix packaging of mozilla-release (#10949)

`MOZ_AUTOMATION` env variable requires us to set a bunch of other
variables to package the build.

browser_patches/firefox/archive.sh

@@ -40,6 +40,8 @@ OBJ_FOLDER="${FF_CHECKOUT_PATH}/obj-build-playwright"
 
 cd "${FF_CHECKOUT_PATH}"
 
+export MH_BRANCH=mozilla-release
+export MOZ_BUILD_DATE=$(date +%Y%m%d%H%M%S)
 if [[ "$2" == "--linux-arm64" ]]; then
   CMD_STRIP=/usr/bin/aarch64-linux-gnu-strip ./mach package
 else