Trust codesign using the certificate

When build_release_nightly calls codesign to sign libzim.7.dylib, it appears to be
hanging forever.
What's most likely happening is that Keychain Access is prompting a password request
without any possibility to answer, given this is running on the CI.

It's unclear whether Keychain Access wants to confirm codesign can access the certificate
or if it is trying to unlock another (System) keychain to find the certificate or key.

This addresses the former.

.github/scripts/common.py

@@ -483,6 +483,8 @@ def notarize_macos_build(project):
     for filepath in filepaths:
         subprocess.check_call(["/usr/bin/codesign", "--force", "--sign",
                                os.getenv("SIGNING_IDENTITY", "no-signing-ident"),
+                               "--keychain",
+                               os.getenv("KEYCHAIN", "no-keychain-path"),
                                str(filepath), "--deep", "--timestamp"], env=os.environ)
 
     # create a zip of the dylibs and upload for notarization