Use Botan 3.1.1 for tests

The all-zero Ed25519 public key is rejected by botan_pubkey_check_key()
when the key is loaded.

Note that Botan 3 requires GCC 11 or CLANG 14, i.e. can't easily be built
on Debian bullseye or Ubuntu 20.04.

The thread-local storage function gets flagged via various botan FFI
functions when using Botan 3, whitelist that instead of all of them.

src/libstrongswan/utils/leak_detective.c

@@ -542,6 +542,8 @@ static char *whitelist[] = {
 	"_IO_file_doallocate",
 	"selinux_check_access",
 	"on_exit",
+	/* glibc thread-local storage triggered primarily by Botan */
+	"__tls_get_addr",
 	/* ignore dlopen, as we do not dlclose to get proper leak reports */
 	"dlopen",
 	"dlerror",
@@ -668,6 +670,7 @@ static char *whitelist[] = {
 	"botan_kdf",
 	/* C++ due to Botan */
 	"__cxa_get_globals",
+	"__cxa_thread_atexit",
 };
 
 /**