Fixes a test when there is no default region on the machine, as is th…

…e case in a GitHub Action.

Signed-off-by: David Venable <[email protected]>

data-prepper-plugins/aws-plugin/src/test/java/org/opensearch/dataprepper/plugins/aws/CredentialsProviderFactoryTest.java

@@ -86,6 +86,8 @@ void providerFromOptions_with_invalid_StsRoleArn_throws(final String stsRoleArn)
     void providerFromOptions_with_StsRoleArn() {
         when(awsCredentialsOptions.getStsRoleArn())
                 .thenReturn(createStsRole());
+        when(awsCredentialsOptions.getRegion())
+                .thenReturn(Region.US_EAST_1);
         final AwsCredentialsProvider awsCredentialsProvider = createObjectUnderTest().providerFromOptions(awsCredentialsOptions);
         assertThat(awsCredentialsProvider, instanceOf(StsAssumeRoleCredentialsProvider.class));
     }