[Infrastructure] Pin actions with SHA and improve workflows (#6249)

* Pin actions with SHA, replace unmaintained, add dependabot for actions

* Update FreeBSD to version 15 for tests

* Use shared actions

* Update sign-pipelines version

.github/workflows/git-town.yml

@@ -3,7 +3,7 @@ name: Git Town
 on:
   pull_request:
     branches:
-      - '**'
+      - "**"
 
 jobs:
   git-town:
@@ -15,7 +15,9 @@ jobs:
       pull-requests: write
 
     steps:
-      - uses: actions/checkout@v4
-      - uses: git-town/action@v1.2.1
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - uses: git-town/action@3d8b878379abb1ee393fb49865a28b4a6c2cd3b0 # v1.2.1
         with:
           skip-single-stacks: true