fix(diagrams): missing quotes for messaging diagram (#5750)

Description
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adds missing quotes for messaging diagram

Motivation and Context
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Rendering fails in github

How Has This Been Tested?
---

What process can a PR reviewer use to test or verify this change?
---

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Breaking Changes
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- [x] None
- [ ] Requires data directory on base node to be deleted
- [ ] Requires hard fork
- [ ] Other - Please specify

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docs/src/diagrams/comms/inbound_messaging.md

@@ -15,7 +15,7 @@ flowchart TD
     A[Start] --> B[1. trigger: Protocol Negotiation /t/msg/0.1]
     B --> C[2. protocols::messaging::InboundMessaging]
     C -->|InboundMessage| D[3. Inbound pipeline]
-    D -->|<threads>| E[4. Inbound DHT middlewares]
+    D -->|"<threads>"| E[4. Inbound DHT middlewares]
     E -->|DecryptedDhtMessage| F[5. Pubsub connector]
     F --o|PeerMessage| G[6. ... Domain subscribers ...]
 ```