Update minSdk values in UtilTest

These were missed when upgrading to both SDK 19 and 21, but they now
cause failures like:

```
Caused by: java.lang.RuntimeException: Failed to parse package buildout/intermediates/apk_for_local_test/debugUnitTest/packageDebugUnitTestForUnitTest/apk-for-local-test.ap_: buildout/intermediates/apk_for_local_test/debugUnitTest/packageDebugUnitTestForUnitTest/apk-for-local-test.ap_ (at Binary XML file line #20): Requires newer sdk version #21 (current version is #19)
    at org.robolectric.shadows.ShadowPackageParser.callParsePackage(ShadowPackageParser.java:61)
    ... 20 more
```

#cherrypick

PiperOrigin-RevId: 670241471

libraries/common/src/test/java/androidx/media3/common/util/UtilTest.java

@@ -1570,7 +1570,7 @@ public void contentEquals_oneNullSparseArrayAndOneNonNullSparseArray_returnsFals
   }
 
   @Test
-  @Config(minSdk = 16) // Specifies the minimum SDK to enforce the test to run with all API levels.
+  @Config(minSdk = 21) // Specifies the minimum SDK to enforce the test to run with all API levels.
   public void contentEquals_sparseArraysWithEqualContent_returnsTrue() {
     SparseArray<Integer> sparseArray1 = new SparseArray<>();
     sparseArray1.put(1, 2);
@@ -1583,7 +1583,7 @@ public void contentEquals_sparseArraysWithEqualContent_returnsTrue() {
   }
 
   @Test
-  @Config(minSdk = 16) // Specifies the minimum SDK to enforce the test to run with all API levels.
+  @Config(minSdk = 21) // Specifies the minimum SDK to enforce the test to run with all API levels.
   public void contentEquals_sparseArraysWithDifferentContents_returnsFalse() {
     SparseArray<Integer> sparseArray1 = new SparseArray<>();
     sparseArray1.put(1, 2);
@@ -1599,7 +1599,7 @@ public void contentEquals_sparseArraysWithDifferentContents_returnsFalse() {
   }
 
   @Test
-  @Config(minSdk = 16) // Specifies the minimum SDK to enforce the test to run with all API levels.
+  @Config(minSdk = 21) // Specifies the minimum SDK to enforce the test to run with all API levels.
   public void contentHashCode_sparseArraysWithEqualContent_returnsEqualContentHashCode() {
     SparseArray<Integer> sparseArray1 = new SparseArray<>();
     sparseArray1.put(1, 2);
@@ -1612,7 +1612,7 @@ public void contentHashCode_sparseArraysWithEqualContent_returnsEqualContentHash
   }
 
   @Test
-  @Config(minSdk = 16) // Specifies the minimum SDK to enforce the test to run with all API levels.
+  @Config(minSdk = 21) // Specifies the minimum SDK to enforce the test to run with all API levels.
   public void contentHashCode_sparseArraysWithDifferentContent_returnsDifferentContentHashCode() {
     // In theory this is not guaranteed though, adding this test to ensure a sensible
     // contentHashCode implementation.