Add additional test case for $$${API_KEY} => $${API_KEY}

Author: jack-berg

sdk-extensions/incubator/src/test/java/io/opentelemetry/sdk/extension/incubator/fileconfig/FileConfigurationParseTest.java

@@ -659,6 +659,7 @@ private static java.util.stream.Stream<Arguments> envVarSubstitutionArgs() {
         Arguments.of("key1: \"${FLOAT}\"\n", mapOf(entry("key1", "1.1"))),
         // Escaped
         Arguments.of("key1: $${STR_1}\n", mapOf(entry("key1", "${STR_1}"))),
+        Arguments.of("key1: $$${STR_1}\n", mapOf(entry("key1", "$${STR_1}"))),
         Arguments.of("key1: \"$${STR_1}\"\n", mapOf(entry("key1", "${STR_1}"))),
         Arguments.of("key1: $${STR_1} ${STR_2}\n", mapOf(entry("key1", "${STR_1} value2"))),
         Arguments.of("key1: $${STR_1} $${STR_2}\n", mapOf(entry("key1", "${STR_1} ${STR_2}"))),