Remove relative date in IndicesRequestCacheIT (#20920) (#20953)

The dates in the test are starting to fall out of the now-10y window. It
should be fine to use a fixed date for the 'from' since the 'to' uses
now.


(cherry picked from commit bbb28cd)

Signed-off-by: Andrew Ross <andrross@amazon.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

server/src/internalClusterTest/java/org/opensearch/indices/IndicesRequestCacheIT.java

@@ -552,7 +552,7 @@ public void testCanCache() throws Exception {
             .setSize(0)
             .setRequestCache(true)
             .setQuery(QueryBuilders.rangeQuery("s").gte("2016-03-20").lte("2016-03-26"))
-            .addAggregation(dateRange("foo").field("s").addRange("now-10y", "now"))
+            .addAggregation(dateRange("foo").field("s").addRange("2016-01-01", "now"))
             .get();
         OpenSearchAssertions.assertAllSuccessful(r5);
         assertThat(r5.getHits().getTotalHits().value(), equalTo(7L));
@@ -575,7 +575,7 @@ public void testCanCache() throws Exception {
             .setSize(0)
             .setRequestCache(true)
             .setQuery(QueryBuilders.rangeQuery("s").gte("2016-03-20").lte("2016-03-26"))
-            .addAggregation(filter("foo", QueryBuilders.rangeQuery("s").from("now-10y").to("now")))
+            .addAggregation(filter("foo", QueryBuilders.rangeQuery("s").from("2016-01-01").to("now")))
             .get();
         OpenSearchAssertions.assertAllSuccessful(r4);
         assertThat(r4.getHits().getTotalHits().value(), equalTo(7L));