Unquarantine clickhouse binary on mac (#5223)

After #5127 (I assume, because this problem came up immediately after
that) macOS Gatekeeper is putting the `clickhouse` binary in quarantine
after download, which means we can't execute it unless we take it out of
quarantine. This is apparently a new thing, as [this
doc](https://github.com/ClickHouse/clickhouse-docs/blob/08d7a329d/knowledgebase/fix-developer-verification-error-in-macos.md)
about how to do that was only [added Jan
9](ClickHouse/clickhouse-docs#1835).

Here I am doing it in the simplest way possible: if mac, then remove
quarantine attr. If anyone has a better way, I'm all ears.

tools/ci_download_clickhouse

@@ -84,6 +84,12 @@ function main
 	# Unpack the tarball into a local directory
 	do_untar "$TARBALL_FILE" "$DEST_DIR"
 
+	# on macOS, we need to take the binary out of quarantine after download
+	# https://github.com/ClickHouse/clickhouse-docs/blob/08d7a329d/knowledgebase/fix-developer-verification-error-in-macos.md
+	if [[ $CIDL_OS == darwin* ]]; then
+		xattr -d com.apple.quarantine "$DEST_DIR/clickhouse"
+	fi
+
 	# Run the binary as a sanity-check.
 	"$DEST_DIR/clickhouse" server --version
 }