Say held updates wait because a walk failed, in the glossary's words

The backlog is held after any failed walk, not only a release, and a check is a pull
request's status; the words said the last release failed its check.

cmd/mesh-controller/plain_words.go

@@ -667,7 +667,7 @@ func moduleNeeds(node string, rs []inventory.ResourceHealth) string {
 // authorised (to-be 46 phases 5 and 6).
 const FromMeshMCPServer = "from the mesh MCP server; this notification cannot do it."
 
-// releaseHeldWords are the plain words of updates held after a release failed its gate: which modules wait,
+// releaseHeldWords are the plain words of updates held after a walk failed: which modules wait,
 // on which machines, and where the operator releases them (ADR 0258: a release is not an acknowledgement, so
 // no notification gives it). Raised with the modules and machines (backlogObservation); the kind's fallback
 // knows neither.
@@ -688,8 +688,8 @@ func releaseHeldWords(modules, machines []string) words {
 	}
 	return words{Headline: headline,
 		Needs: "release them " + FromMeshMCPServer,
-		Explanation: fmt.Sprintf("%s%s wait for a person to release them, because the last release failed its "+
-			"check. They are not delivered until then, and stay held if you leave them.", what, where),
+		Explanation: fmt.Sprintf("%s%s wait for a person to release them, because the last walk failed."+
+			" They are not delivered until then, and stay held if you leave them.", what, where),
 		Resolved: "Resolved: the held updates are released"}
 }