Fixing flaky endtoend/tablegc tests

[shlomi-noach]

Description

Fixes #7878

Checklist

• Should this PR be backported?
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving
• VReplication
• Cluster Management
• Build/CI
• VTAdmin

[shlomi-noach]

Example for failed test: https://github.com/vitessio/vitess/runs/2421562090?check_suite_focus=true (shard named 27 now renamed in this PR to tabletmanager_tablegc):

== RUN   TestPopulateTable
--- PASS: TestPopulateTable (0.02s)
=== RUN   TestHold
--- PASS: TestHold (15.03s)
=== RUN   TestEvac
--- PASS: TestEvac (20.03s)
=== RUN   TestDrop
--- PASS: TestDrop (20.03s)
=== RUN   TestPurge
    tablegc_test.go:331: 
        	Error Trace:	tablegc_test.go:331
        	Error:      	Should be false
        	Test:       	TestPurge
    tablegc_test.go:337: 
        	Error Trace:	tablegc_test.go:337
        	Error:      	Should be true
        	Test:       	TestPurge
    tablegc_test.go:123: 
        	Error Trace:	tablegc_test.go:123
        	            				tablegc_test.go:338
        	Error:      	Should NOT be empty, but was 
        	Test:       	TestPurge
--- FAIL: TestPurge (65.03s)
FAIL
FAIL	vitess.io/vitess/go/test/endtoend/tabletmanager/tablegc	146.848s
FAIL

[shlomi-noach]

This should be good to go. Basically just incrmented some sleep time to let the mechnism do its expected work.

[harshit-gangal]

I think this needs to be removed "Run endtoend tests on Cluster (27) Expected — Waiting for status to be reported"

[shlomi-noach]

I think this needs to be removed "Run endtoend tests on Cluster (27) Expected — Waiting for status to be reported"

Indeed. Thank you!

[shlomi-noach]

Removed Run endtoend tests on Cluster (27) from being Required. Merging and then adding tabletmanager_tablegc as Required.