[Fix] Increase event polling retries in test (#1280)

### Description

Increases the event polling timeout for the end-to-end tests. This
resolves the flakiness after the webhook event change went in.

### Context

Events take slightly longer to post now that we are additionally sending
the events to a channel.

### Testing

- `./gradlew test`

### Documentation

N/A

### Known limitations

N/A

essential-tests/src/testFixtures/kotlin/org/stellar/anchor/platform/e2etest/Sep24End2EndTests.kt

@@ -269,7 +269,7 @@ open class Sep24End2EndTests : AbstractIntegrationTests(TestConfig()) {
     txnId: String,
     count: Int
   ): List<Sep24GetTransactionResponse>? {
-    var retries = 5
+    var retries = 30
     var callbacks: List<Sep24GetTransactionResponse>? = null
     while (retries > 0) {
       callbacks = walletServerClient.getCallbacks(txnId, Sep24GetTransactionResponse::class.java)
@@ -286,7 +286,7 @@ open class Sep24End2EndTests : AbstractIntegrationTests(TestConfig()) {
     txnId: String,
     count: Int
   ): List<SendEventRequest>? {
-    var retries = 5
+    var retries = 30
     var events: List<SendEventRequest>? = null
     while (retries > 0) {
       events = anchorReferenceServerClient.getEvents(txnId)

essential-tests/src/testFixtures/kotlin/org/stellar/anchor/platform/e2etest/Sep31End2EndTests.kt

@@ -168,7 +168,7 @@ open class Sep31End2EndTests : AbstractIntegrationTests(TestConfig()) {
     txnId: String,
     count: Int
   ): List<Sep31GetTransactionResponse>? {
-    var retries = 5
+    var retries = 30
     var callbacks: List<Sep31GetTransactionResponse>? = null
     while (retries > 0) {
       callbacks = walletServerClient.getCallbacks(txnId, Sep31GetTransactionResponse::class.java)
@@ -185,7 +185,7 @@ open class Sep31End2EndTests : AbstractIntegrationTests(TestConfig()) {
     txnId: String,
     count: Int
   ): List<SendEventRequest>? {
-    var retries = 5
+    var retries = 30
     var events: List<SendEventRequest>? = null
     while (retries > 0) {
       events = anchorReferenceServerClient.getEvents(txnId)