Bump envoy version to 1.25 and 1.26

[nak3]

As per title, this patch bumps envoy version to 1.25 and 1.26.

Release Note

Kourier Gateway uses envoy 1.25 by default.

[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, nak3

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[codecov]

Codecov Report

Merging #1096 (2e76251) into main (a531308) will not change coverage.
Report is 13 commits behind head on main.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1096   +/-   ##
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  Coverage   80.00%   80.00%           
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  Files          18       18           
  Lines        1430     1430           
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  Hits         1144     1144           
  Misses        229      229           
  Partials       57       57