Don't allow underscores in TLD ROID suffixes

Per ICANN it's a disallowed character.

Author: CydeWeys

core/src/main/java/google/registry/model/tld/Tld.java

@@ -1034,7 +1034,7 @@ public Builder setEapFeeSchedule(ImmutableSortedMap<DateTime, Money> eapFeeSched
       return this;
     }
 
-    public static final Pattern ROID_SUFFIX_PATTERN = Pattern.compile("^[A-Z\\d_]{1,8}$");
+    public static final Pattern ROID_SUFFIX_PATTERN = Pattern.compile("^[A-Z\\d]{1,8}$");
 
     public Builder setRoidSuffix(String roidSuffix) {
       checkArgument(

core/src/test/java/google/registry/model/tld/TldTest.java

@@ -751,7 +751,7 @@ void testFailure_roidSuffixTooLong() {
         assertThrows(
             IllegalArgumentException.class,
             () -> Tld.get("tld").asBuilder().setRoidSuffix("123456789"));
-    assertThat(e).hasMessageThat().isEqualTo("ROID suffix must be in format ^[A-Z\\d_]{1,8}$");
+    assertThat(e).hasMessageThat().isEqualTo("ROID suffix must be in format ^[A-Z\\d]{1,8}$");
   }
 
   @Test
@@ -766,6 +766,12 @@ void testFailure_roidSuffixContainsInvalidCharacters() {
         IllegalArgumentException.class, () -> Tld.get("tld").asBuilder().setRoidSuffix("ABC-DEF"));
   }
 
+  @Test
+  void testFailure_roidSuffixContainsUnderscores() {
+    assertThrows(
+        IllegalArgumentException.class, () -> Tld.get("tld").asBuilder().setRoidSuffix("ABC_DEF"));
+  }
+
   @Test
   void testSuccess_setDefaultPromoTokens() {
     Tld registry = Tld.get("tld");