rename eddsa_sig.c for autogeneration

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27859)

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