Summary:
Since PHP 8.1, conversion from float to integer should be explicit.
https://wiki.php.net/rfc/implicit-float-int-deprecate
According to `phlog`, the alpha channel value of the automatically created user
avatar image for a new user account sometimes is a float.
Thus always `round()` the alpha channel value to be an integer.
Closes T15375
Test Plan: Applied this change, created five user accounts via http://phorge.localhost/people/new/standard/ , and each resulting alpha value in `PhabricatorFilesComposeAvatarBuiltinFile.php` was an integer according to `phlog` (see corresponding Maniphest task). Rendering of each new user page always succeeded.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15375
Differential Revision: https://we.phorge.it/D25209
c2856b479f