Fix potential memory leak in OSSL_HPKE_CTX_new()

ctx->propq is a duplicated string, but the error code does not free
the duplicated string's memory. If e.g. EVP_CIPHER_fetch() fails then
we can leak the string's memory.

Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/25812)

crypto/hpke/hpke.c

@@ -841,6 +841,7 @@ OSSL_HPKE_CTX *OSSL_HPKE_CTX_new(int mode, OSSL_HPKE_SUITE suite, int role,
 
  err:
     EVP_CIPHER_free(ctx->aead_ciph);
+    OPENSSL_free(ctx->propq);
     OPENSSL_free(ctx);
     return NULL;
 }