fix(make): fail the protoc download on an HTTP error (#12187)

`make protoc` fetched the protoc release with `curl -L` and no `-f`. When
GitHub answered with an error, curl saved the error page as protoc.zip and
exited 0, and the build then failed at unzip with "cannot find zipfile
directory", which points at the archive rather than at the download.

This happened for real: GitHub answered a CI cluster with a 504 for release
downloads for over an hour, and every backend build that runs
`make protogen-go` failed with the unzip message.

`-f` makes curl fail on the HTTP status and write nothing, so the error names
the real cause. `--retry-all-errors` also retries HTTP errors, which rides
out a short blip; a longer outage still fails, now with the right message.


Assisted-by: Claude:claude-opus-5 [Claude Code]

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

Makefile

@@ -576,7 +576,7 @@ protoc:
 	  echo "Unsupported OS: $$OS_NAME"; exit 1; \
 	fi; \
 	URL=https://github.com/protocolbuffers/protobuf/releases/download/v31.1/$$FILE; \
-	curl -L $$URL -o protoc.zip && \
+	curl -fsSL --retry 5 --retry-all-errors --retry-delay 5 $$URL -o protoc.zip && \
 	unzip -j -d $(CURDIR) protoc.zip bin/protoc && rm protoc.zip
 
 .PHONY: protogen-go