extrakeys: Init empty experimental module

This is to prepare for xonly_pubkeys and keypairs.

src/tests.c

@@ -5306,6 +5306,10 @@ void run_ecdsa_openssl(void) {
 # include "modules/recovery/tests_impl.h"
 #endif
 
+#ifdef ENABLE_MODULE_EXTRAKEYS
+# include "modules/extrakeys/tests_impl.h"
+#endif
+
 void run_memczero_test(void) {
     unsigned char buf1[6] = {1, 2, 3, 4, 5, 6};
     unsigned char buf2[sizeof(buf1)];
@@ -5612,6 +5616,10 @@ int main(int argc, char **argv) {
     run_recovery_tests();
 #endif
 
+#ifdef ENABLE_MODULE_EXTRAKEYS
+    run_extrakeys_tests();
+#endif
+
     /* util tests */
     run_memczero_test();