CI: Print certificates and expiry dates

.github/workflows/build.yml

@@ -241,7 +241,13 @@ jobs:
           security set-keychain-settings Mixxx.keychain
           echo "CMAKE_ARGS_EXTRA=${CMAKE_ARGS_EXTRA} -DAPPLE_CODESIGN_IDENTITY=${APPLE_CODESIGN_IDENTITY}" >> "${GITHUB_ENV}"
 
-          # Print code signing identities
+          # https://unix.stackexchange.com/questions/696224/using-openssl-to-display-all-certificates-of-a-pem-file
+          # https://stackoverflow.com/questions/16576537/how-can-i-find-exactly-what-my-codesign-identity-is
+
+          echo "==> Available certificates"
+          security find-certificate -a -p Mixxx.keychain | while openssl x509 -noout -text; do :; done | grep "Certificate\|Validity\|Subject\|Not"
+
+          echo "==> Available code signing identities"
           security find-identity -v -p codesigning Mixxx.keychain
 
       - name: "[Windows] Set up Windows code signing"