Change 'invalid map' warning to be silent. (#12748)

The warning is very prominent and persistent.

This update logs the warning in the background without a pop-up.

A prominent popup would be okay if it were easily fixed (eg:
the offending map deleted). Short of that, we're just making the
warning quiet.

game-app/map-data/src/main/java/org/triplea/map/description/file/MapDescriptionYamlReader.java

@@ -63,8 +63,8 @@ static Optional<MapDescriptionYaml> parse(final Path ymlFile, final InputStream
               .build();
 
       if (!mapDescriptionYaml.isValid(ymlFile)) {
-        log.warn(
-            "Invalid map description YML (map.yml) file detected: {}\n"
+        log.info(
+            "Warning: Invalid map description YML (map.yml) file detected: {}\n"
                 + "Check the file carefully and correct any mistakes.\n"
                 + "If this is a map you downloaded, please contact TripleA.\n"
                 + "Data parsed:\n"
@@ -75,8 +75,8 @@ static Optional<MapDescriptionYaml> parse(final Path ymlFile, final InputStream
       }
       return Optional.of(mapDescriptionYaml);
     } catch (final ClassCastException | InvalidYamlFormatException e) {
-      log.warn(
-          "Invalid map description YML (map.yml) file detected: {}.\n"
+      log.info(
+          "Warning: Invalid map description YML (map.yml) file detected: {}.\n"
               + "If this is a map you downloaded, please contact TripleA.\n"
               + "{}",
           ymlFile.toAbsolutePath(),