ci: increase timeout for tests on OpenBSD

[cakebaker]

Recently, the tests job on OpenBSD started to run into timeouts. This PR increases the timeout from 60 minutes to 75 minutes.

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/id/smack was skipped on 'main' but is now failing.
Note: The gnu test tests/mkdir/smack-no-root was skipped on 'main' but is now failing.
Note: The gnu test tests/mkdir/smack-root was skipped on 'main' but is now failing.

[cakebaker]

Closing this PR as the issue is a full disk: the runner stops and waits for the timeout. From the log it is visible that for half an hour nothing happens:

2025-12-29T05:37:53.2373228Z ##[warning]You are running out of disk space. The runner will stop working when the machine runs out of disk space. Free space left: 16 MB
2025-12-29T06:08:19.5464639Z ##[error]The operation was canceled.

[oech3]

Is #9277 helpful?