use a public url for git submodules (#499)

When pulling `RSA` with a `[patch.crates-io]`, the CI runner doesn't
carry an SSH key with github and fails to clone the submodules.

This changes the `[email protected]` to an `https://github.com` to allow
anonymous clones.

Author: baloo

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "thirdparty/wycheproof"]
 	path = thirdparty/wycheproof
-	url = git@github.com:C2SP/wycheproof
+	url = https://github.com/C2SP/wycheproof.git