.github: nightly job to verify if toolchain directives are in sync

Signed-off-by: Madhav Jivrajani <madhav.jiv@gmail.com>

.github/workflows/toolchain-directive-nightly.yaml

@@ -0,0 +1,22 @@
+---
+name: Go Toolchain Directive Nightly
+permissions: read-all
+on:
+  schedule:
+    - cron: '25 9 * * *' # runs every day at 09:25 UTC
+
+  # workflow_dispatch enables manual testing of this job by maintainers
+  workflow_dispatch:
+
+jobs:
+  run:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+      - id: goversion
+        run: echo "goversion=$(cat .go-version)" >> "$GITHUB_OUTPUT"
+      - uses: actions/setup-go@0c52d547c9bc32b1aa3301fd7a9cb496313a4491 # v5.0.0
+        with:
+          go-version: ${{ steps.goversion.outputs.goversion }}
+      - id: verifytoolchain
+        run: scripts/verify_toolchain_directive.sh