[ci] Pin Discord webhook action to specific commit sha (#32649)

Pins the discord webhook action to
`86dc739f3f165f16dadc5666051c367efa1692f4`, which is what the v6 tag
points to.
---
[//]: # (BEGIN SAPLING FOOTER)
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with [ReviewStack](https://reviewstack.dev/facebook/react/pull/32649).
* #32650
* __->__ #32649
* #32648

.github/workflows/compiler_discord_notify.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Discord Webhook Action
-        uses: tsickert/discord-webhook@v6.0.0
+        uses: tsickert/discord-webhook@86dc739f3f165f16dadc5666051c367efa1692f4
         with:
           webhook-url: ${{ secrets.COMPILER_DISCORD_WEBHOOK_URL }}
           embed-author-name: ${{ github.event.pull_request.user.login }}

.github/workflows/runtime_discord_notify.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Discord Webhook Action
-        uses: tsickert/discord-webhook@v6.0.0
+        uses: tsickert/discord-webhook@86dc739f3f165f16dadc5666051c367efa1692f4
         with:
           webhook-url: ${{ secrets.DISCORD_WEBHOOK_URL }}
           embed-author-name: ${{ github.event.pull_request.user.login }}

.github/workflows/runtime_releases_from_npm_manual.yml

@@ -44,7 +44,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Discord Webhook Action
-        uses: tsickert/discord-webhook@v6.0.0
+        uses: tsickert/discord-webhook@86dc739f3f165f16dadc5666051c367efa1692f4
         with:
           webhook-url: ${{ secrets.DISCORD_WEBHOOK_URL }}
           embed-author-name: ${{ github.event.sender.login }}