ci(fix): fix extra output in MATS Env slack message output

[joshmarinacci]

Description:

The slack template for MATS Env failures is producing erroneous output due to a malformed template.

Related issue(s):

Fixes # #26841

Notes for reviewer:

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[lfdt-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff            @@
##               main   #26864   +/-   ##
=========================================
  Coverage     70.46%   70.46%           
  Complexity    11690    11690           
=========================================
  Files          2583     2583           
  Lines        108413   108413           
  Branches      12135    12134    -1     
=========================================
  Hits          76397    76397           
  Misses        28021    28021           
  Partials       3995     3995           

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