TEZ-4736: Fix flaky TestMRRJobsDAGApi.testMultipleMRRSleepJobViaSession

[maheshrajus]

Root causes and fixes:

TestMRRJobsDAGApi.testMultipleMRRSleepJobViaSession (DAG SUCCEEDED ≠ AM READY)
In session mode, DAG reaching SUCCEEDED does not mean the AM session has
transitioned back to READY. there is a short cleanup window.
On slow CI the subsequent getAppMasterStatus() call returned RUNNING instead of READY.

Add tezSession.waitTillReady() before each assertEquals(READY, ...) so
the test waits for the actual state transition.

[tez-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	8m 30s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	detsecrets	0m 0s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 1 new or modified test files.
			_ master Compile Tests _
+1 💚	mvninstall	5m 3s		master passed
+1 💚	compile	4m 0s		master passed
+1 💚	checkstyle	0m 32s		master passed
+1 💚	javadoc	0m 27s		master passed
+0 🆗	spotbugs	0m 53s		tez-tests in master has 6 extant spotbugs warnings.
			_ Patch Compile Tests _
+1 💚	mvninstall	3m 59s		the patch passed
+1 💚	codespell	1m 47s		No new issues.
+1 💚	compile	3m 57s		the patch passed
+1 💚	javac	3m 57s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 27s		the patch passed
+1 💚	javadoc	0m 26s		the patch passed
+1 💚	spotbugs	1m 3s		the patch passed
			_ Other Tests _
+1 💚	unit	71m 46s		root in the patch passed.
+1 💚	asflicense	0m 31s		The patch does not generate ASF License warnings.
		105m 3s

Subsystem	Report/Notes
Docker	ClientAPI=1.55 ServerAPI=1.55 base: https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-521/1/artifact/out/Dockerfile
Optional Tests	dupname compile unit asflicense javac javadoc spotbugs checkstyle codespell detsecrets
uname	Linux 56c37664b37c 5.15.0-181-generic #191-Ubuntu SMP Fri May 22 19:09:02 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	tez-personality.sh
git revision	master / 4bccf3a
Default Java	Eclipse Adoptium-21.0.11+10-LTS
Test Results	https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-521/1/testReport/
Max. process+thread count	1483 (vs. ulimit of 5500)
modules	C: tez-tests U: tez-tests
Console output	https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-521/1/console
versions	git=2.43.0 maven=3.9.15 spotbugs=4.9.3 codespell=2.4.1
Powered by	Apache Yetus 0.15.1 https://yetus.apache.org

This message was automatically generated.