chore: correct misspelling in lambda expression

Observed a misspelling in the JwtAuthenticationTestUtils.java.ejs template using the
JwtClaimsSet.builder setting claims via a Lambda expression.

s/customClain/customClaim

Fixes jhipster#25079

generators/server/templates/src/test/java/_package_/security/jwt/JwtAuthenticationTestUtils.java.ejs

@@ -77,7 +77,7 @@ public class JwtAuthenticationTestUtils {
             .issuedAt(now)
             .expiresAt(now.plusSeconds(60))
             .subject(user)
-            .claims(customClain -> customClain.put(AUTHORITIES_KEY, Collections.singletonList("ROLE_ADMIN")))
+            .claims(customClaim -> customClaim.put(AUTHORITIES_KEY, Collections.singletonList("ROLE_ADMIN")))
             .build();
 
         JwsHeader jwsHeader = JwsHeader.with(JWT_ALGORITHM).build();