keyring: verify runc.keyring has legitimate maintainer keys

These checks ensure that all of the keys in the runc.keyring list are
actually the keys of the specified user and that the users themselves
are actually maintainers.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

.github/workflows/validate.yml

@@ -11,6 +11,12 @@ env:
   GO_VERSION: 1.19.x
 
 jobs:
+  keyring:
+    runs-on: ubuntu-22.04
+    steps:
+    - uses: actions/checkout@v3
+    - name: check runc.keyring
+      run: make validate-keyring
 
   lint:
     runs-on: ubuntu-20.04