Use correct Sender on webhook change title

[Gusted]

As title, thanks to @mscherer for pointing out the incorrect code.

• Resolves Wrong user on Issue title change for Matrix webhook #17788

[codecov-commenter]

Codecov Report

Merging #17791 (4f51fc3) into main (7743f13) will increase coverage by 0.03%.
The diff coverage is 52.26%.

@@            Coverage Diff             @@
##             main   #17791      +/-   ##
==========================================
+ Coverage   45.54%   45.58%   +0.03%     
==========================================
  Files         807      808       +1     
  Lines       89859    89982     +123     
==========================================
+ Hits        40930    41016      +86     
- Misses      42381    42423      +42     
+ Partials     6548     6543       -5     

Impacted Files	Coverage Δ
cmd/admin.go	0.00% <0.00%> (ø)
cmd/web_https.go	0.00% <ø> (ø)
models/access.go	70.54% <ø> (-0.50%)	⬇️
models/ssh_key_authorized_keys.go	58.82% <ø> (ø)
models/user_email.go	43.41% <0.00%> (-3.65%)	⬇️
routers/api/v1/org/member.go	18.94% <0.00%> (-0.84%)	⬇️
routers/api/v1/repo/star.go	0.00% <0.00%> (ø)
routers/api/v1/user/follower.go	0.00% <0.00%> (ø)
routers/api/v1/user/user.go	52.50% <0.00%> (ø)
routers/private/serv.go	39.57% <0.00%> (-0.86%)	⬇️
... and 55 more

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[lunny]

Please send backport to v1.15

[Gusted]

Please send backport to v1.15

#17792