Update release_prep.sh

Fix a minor syntax error in markdown

.github/workflows/release_prep.sh

diff --git a/.github/workflows/release_prep.sh b/.github/workflows/release_prep.sh
index 8fc1749..60b6842 100755
--- a/.github/workflows/release_prep.sh
+++ b/.github/workflows/release_prep.sh
@@ -39,5 +39,5 @@
     strip_prefix = "${PREFIX}",
     url = "https://github.com/bazelbuild/rules_proto/releases/download/${TAG}/${ARCHIVE}",
 )
-\`\`\`starlark
+\`\`\`
 EOF