valgrind: suppress memory leaks in libssh2_session_handshake

On Ubuntu, the combination of libgcrypt and libssh2 is quite old and
known to contain memory leaks. We thus have several functions listed in
our suppressions file that are known to leak. Due to a recent update of
libssh2 or libgcrypt, there now are new memory leaks caused by
libssh2_session_handshake and libssh2_init that cause the CI to fail.

Add a new suppression to fix the issue.

Author: pks-t

script/valgrind.supp

@@ -55,6 +55,15 @@
 	fun:curl_global_init
 }
 
+{
+	ignore-libssh2-init
+	Memcheck:Leak
+	...
+	fun:gcry_control
+	fun:libssh2_init
+	...
+}
+
 {
 	ignore-libssh2-gcrypt-control-leak
 	Memcheck:Leak
@@ -103,6 +112,17 @@
 	obj:*libssh2.so*
 }
 
+{
+	ignore-libssh2-gcrypt-session-handshake
+	Memcheck:Leak
+	...
+	obj:*libgcrypt.so*
+	obj:*libssh2.so*
+	obj:*libssh2.so*
+	fun:libssh2_session_handshake
+	...
+}
+
 {
 	ignore-noai6ai_cached-double-free
 	Memcheck:Free