[CI] Change slack channel (#682) backport for 7.10.x

[v1v]

Backports the following commits to 7.10.x:

• [CI] Change slack channel ([CI] Change slack channel #682)

[elasticmachine]

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• Build Cause: Pull request #685 opened

• • Start Time: 2021-02-01T15:57:05.106+0000

• Duration: 25 min 22 sec

• Commit: ae6af7a

Test stats 🧪

Test	Results
Failed	0
Passed	111
Skipped	11
Total	122

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Test stats 🧪

Test	Results
Failed	0
Passed	111
Skipped	11
Total	122

[EricDavisX]

lgtm; thanks much