.github: checkout submodules in regression.yml

It doesn't look like the regression suites updates the 9pm submodule,
in this commit we attempt to fix this.

Signed-off-by: Richard Alpe <richard@bit42.se>

.github/workflows/regression.yml

@@ -19,6 +19,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
+        with:
+          submodules: 'true'
       - name: Set Build Variables
         id: vars
         run: |