chore: Pin external actions using hashes (#2019)

Note: I used exactly the version which are already being used (didn't
update anything).
Updates will come when we merge https://github.com/XRPLF/clio/pull/2018

.github/workflows/clang-tidy.yml

@@ -89,7 +89,7 @@ jobs:
 
             List of the issues found: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}/
 
-      - uses: crazy-max/ghaction-import-gpg@v6
+      - uses: crazy-max/ghaction-import-gpg@e89d40939c28e39f97cf32126055eeae86ba74ec #v6.3.0
         if: ${{ steps.run_clang_tidy.outcome != 'success' }}
         with:
           gpg_private_key: ${{ secrets.ACTIONS_GPG_PRIVATE_KEY }}
@@ -99,7 +99,7 @@ jobs:
 
       - name: Create PR with fixes
         if: ${{ steps.run_clang_tidy.outcome != 'success' }}
-        uses: peter-evans/create-pull-request@v7
+        uses: peter-evans/create-pull-request@271a8d0340265f705b14b6d32b9829c1cb33d45e #v7.0.8
         env:
           GH_REPO: ${{ github.repository }}
           GH_TOKEN: ${{ github.token }}