Add Tomas Mraz key to release key fingerprints

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18138)
diff --git a/doc/fingerprints.txt b/doc/fingerprints.txt
index 4a8fc8e..9065a5a 100644
--- a/doc/fingerprints.txt
+++ b/doc/fingerprints.txt
@@ -20,3 +20,6 @@
 
 Paul Dale:
 1B72 6772 1033 CC88 A531 5EF5 5359 C4D8 443B 383B
+
+Tomáš Mráz:
+A21F AB74 B008 8AA3 6115 2586 B8EF 1A6B A9DA 2D5C