add semgrep for github workflows

.github/linters/semgrep/pull-request-target-code-checkout.yaml

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+rules:
+  - id: pull-request-target-code-checkout
+    languages:
+      - yaml
+    message: This GitHub Actions workflow file uses `pull_request_target` and checks
+      out code from the incoming pull request. When using `pull_request_target`,
+      the Action runs in the context of the target repository, which includes
+      access to all repository secrets. Please ensure you have `permission-check`
+      enabled for the jobs that check out code. Please see
+      https://securitylab.github.com/research/github-actions-preventing-pwn-requests/
+      for additional mitigations.
+    metadata:
+      category: security
+      owasp:
+        - A01:2021 - Broken Access Control
+      cwe:
+        - "CWE-913: Improper Control of Dynamically-Managed Code Resources"
+      references:
+        - https://securitylab.github.com/research/github-actions-preventing-pwn-requests/
+        - https://github.com/justinsteven/advisories/blob/master/2021_github_actions_checkspelling_token_leak_via_advice_symlink.md
+      technology:
+        - github-actions
+      subcategory:
+        - audit
+      likelihood: MEDIUM
+      impact: LOW
+      confidence: MEDIUM
+      license: Commons Clause License Condition v1.0[LGPL-2.1-only]
+      vulnerability_class:
+        - Code Injection
+    patterns:
+      - pattern-either:
+          - pattern-inside: |
+              on:
+                ...
+                pull_request_target: ...
+                ...
+              ...
+          - pattern-inside: |
+              on: [..., pull_request_target, ...]
+              ...
+          - pattern-inside: |
+              on: pull_request_target
+              ...
+      - pattern-inside: |
+          jobs:
+            ...
+            $JOBNAME:
+              ...
+      - pattern-not-inside: |
+          needs: [permission-check]
+          ...
+      - pattern: |
+          ...
+          uses: "$ACTION"
+      - metavariable-regex:
+          metavariable: $ACTION
+          regex: actions/checkout@.*
+    severity: WARNING

.github/workflows/semgrep.yaml

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+name: Semgrep
+
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - '.github/**'
+
+jobs:
+  semgrep:
+    name: semgrep/ci
+    runs-on: ubuntu-latest
+
+    container:
+      image: returntocorp/semgrep
+
+    # Skip any PR created by dependabot to avoid permission issues:
+    if: (github.actor != 'dependabot[bot]')
+
+    steps:
+      - uses: actions/checkout@v3
+      - run: semgrep ci
+        env:
+           SEMGREP_RULES: >-
+             ./.github/linters/semgrep/pull-request-target-code-checkout.yaml