fix: flaky test issue due to AbortedException. (#2925)

* fix: prevent illegal negative timeout values into thread sleep() method while retrying exceptions in unit tests.

* For details on issue see - #2206

* Fixing lint issues.

* fix: flaky test issue due to AbortedException.

* chore: remove assertion.

Author: arpan14

google-cloud-spanner/src/test/java/com/google/cloud/spanner/it/ITTransactionTest.java

@@ -298,7 +298,6 @@ public void readAbort() throws Exception {
                           } catch (SpannerException e) {
                             if (e.getErrorCode() == ErrorCode.ABORTED) {
                               assertThat(e).isInstanceOf(AbortedException.class);
-                              assertThat(e.getRetryDelayInMillis()).isNotEqualTo(-1L);
                             }
                             throw new RuntimeException("Swallowed exception: " + e.getMessage());
                           }
@@ -338,7 +337,6 @@ public void readAbort() throws Exception {
                           } catch (SpannerException e) {
                             if (e.getErrorCode() == ErrorCode.ABORTED) {
                               assertThat(e).isInstanceOf(AbortedException.class);
-                              assertThat(e.getRetryDelayInMillis()).isNotEqualTo(-1L);
                             }
                             throw new RuntimeException("Swallowed exception: " + e.getMessage());
                           }