[Release 1.28] Bump flannel version to v0.25.2

[thomasferrandiz]

Backport: #10146
Issue: #10218

[codecov]

Codecov Report

Attention: Patch coverage is 48.71795% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 35.84%. Comparing base (a11e446) to head (695192e).

Files	Patch %	Lines
pkg/agent/flannel/flannel.go	48.71%	10 Missing and 10 partials ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.28   #10221      +/-   ##
================================================
- Coverage         42.69%   35.84%   -6.86%     
================================================
  Files               158      155       -3     
  Lines             16414    13895    -2519     
================================================
- Hits               7008     4980    -2028     
+ Misses             8167     7945     -222     
+ Partials           1239      970     -269     

Flag	Coverage Δ
e2etests	35.84% <48.71%> (-9.97%)	⬇️
unittests	?

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