Fix spurious tab in docker-agentgateway echo message

[Copilot]

Description

The docker-agentgateway make target had a stray tab character embedded mid-word in its echo string, producing garbled output ("Building custom age nt gateway image...").

Change Type

/kind fix

Changelog

NONE

Original prompt

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This section details on the original issue you should resolve

<issue_title>Remove random whitespace in the docker-agentgateway make target</issue_title>
<issue_description>```make

Build custom agent gateway image with npx/uvx support

.PHONY: docker-agentgateway
docker-agentgateway: ## Build the custom agent gateway image
@echo "Building custom age nt gateway image..."
$(DOCKER_BUILDER) build $(DOCKER_BUILD_ARGS) -f docker/agentgateway.Dockerfile -t $(DOCKER_REGISTRY)/$(DOCKER_REPO)/arctl-agentgateway:$(VERSION) .
echo "✓ Agent gateway image built successfully";

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Remove random whitespace in the docker-agentgateway make target #378

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[timflannagan]

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[Copilot]

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Updated the PR description to follow the template (Description, Change Type, Changelog sections).