🔄 Update schema URL to v0.68.1 (#3570)

## Schema URL Update

Updates the MCP Gateway JSON schema validation URL from `v0.67.3` to
`v0.68.1`.

### Files Changed

- `internal/config/rules/rules.go` — `SchemaURL` constant updated to
`v0.68.1`
- `internal/config/validation_schema_test.go` — hardcoded schema URL
updated to `v0.68.1`

### Why

Pinning to a specific release tag ensures reproducible, deterministic
configuration validation — the schema won't silently change between
runs.

### Release Notes

See the [gh-aw release
notes](https://github.com/github/gh-aw/releases/tag/v0.68.1) for changes
in this schema version.




> [!NOTE]
> <details>
> <summary>🔒 Integrity filter blocked 1 item</summary>
>
> The following item were blocked because they don't meet the GitHub
integrity level.
>
> -
[https://github.com/github/gh-aw/releases/tag/v0.68.1](https://github.com/github/gh-aw/releases/tag/v0.68.1)
`get_latest_release`: has lower integrity than agent requires. The agent
cannot read data with integrity below "unapproved".
>
> To allow these resources, lower `min-integrity` in your GitHub
frontmatter:
>
> ```yaml
> tools:
>   github:
>     min-integrity: approved  # merged | approved | unapproved | none
> ```
>
> </details>


> Generated by [Nightly Schema
Updater](https://github.com/github/gh-aw-mcpg/actions/runs/24282422674/agentic_workflow)
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> - [x] expires <!-- gh-aw-expires: 2026-04-18T12:29:18.149Z --> on Apr
18, 2026, 12:29 PM UTC

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<!-- gh-aw-expires-type: pull-request -->

<!-- gh-aw-workflow-id: nightly-schema-updater -->

Author: lpcox

internal/config/rules/rules.go

@@ -12,7 +12,7 @@ var log = logger.New("config:rules")
 // Documentation URL constants
 const (
 	ConfigSpecURL = "https://github.com/github/gh-aw/blob/main/docs/src/content/docs/reference/mcp-gateway.md"
-	SchemaURL     = "https://raw.githubusercontent.com/github/gh-aw/v0.67.3/docs/public/schemas/mcp-gateway-config.schema.json"
+	SchemaURL     = "https://raw.githubusercontent.com/github/gh-aw/v0.68.1/docs/public/schemas/mcp-gateway-config.schema.json"
 )
 
 // ValidationError represents a configuration validation error with context.

internal/config/validation_schema_test.go

@@ -580,7 +580,7 @@ func TestEnhancedErrorMessages(t *testing.T) {
 				"Location:",
 				"Error:",
 				"Details:",
-				"https://raw.githubusercontent.com/github/gh-aw/v0.67.3/docs/public/schemas/mcp-gateway-config.schema.json",
+				"https://raw.githubusercontent.com/github/gh-aw/v0.68.1/docs/public/schemas/mcp-gateway-config.schema.json",
 			},
 		},
 		{