argon2: rename C file for conversion to generated param name decoding

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27923)

diff --git a/providers/implementations/kdfs/argon2.c b/providers/implementations/kdfs/argon2.c.in
similarity index 100%
rename from providers/implementations/kdfs/argon2.c
rename to providers/implementations/kdfs/argon2.c.in