ci: re-enable signed-off-by check on workflows

Enable commit signed-off-by check like previously done on Travis-CI.

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>
diff --git a/.github/workflows/mynewt.yaml b/.github/workflows/mynewt.yaml
index 7a9a062..576c1d3 100644
--- a/.github/workflows/mynewt.yaml
+++ b/.github/workflows/mynewt.yaml
@@ -7,12 +7,17 @@
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
     - name: Print the environment
       run: |
         uname -a
         lscpu
         free
         pwd
+    - name: Signed commit check
+      run: |
+        ./ci/check-signed-off-by.sh
     - name: Mynewt install
       run: |
         ./ci/mynewt_install.sh
diff --git a/.github/workflows/sim.yaml b/.github/workflows/sim.yaml
index 1b6177b..b0c5b0d 100644
--- a/.github/workflows/sim.yaml
+++ b/.github/workflows/sim.yaml
@@ -27,6 +27,7 @@
     steps:
     - uses: actions/checkout@v2
       with:
+        fetch-depth: 0
         submodules: recursive
     - name: Print the environment
       run: |
@@ -34,6 +35,9 @@
         lscpu
         free
         pwd
+    - name: Signed commit check
+      run: |
+        ./ci/check-signed-off-by.sh
     - name: Install stable Rust
       uses: actions-rs/toolchain@v1
       with: