Make a small grammatical adjustment

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

The original form of the phrase - «The other option is to specifically
checking if a session has expired after the session is started.» - is
not entirely grammatically correct, as the infinitive form of «to check»
shall normally be used, or the gerund form, which is the form used in
this commit.
FTR, English is not my native language either.

Actually, yes, as I wrote it in the commit message and PR description, I think both the infinitive form and the gerund form are grammatically correct, and, in this context, either may be used as subject complement (but I might also be wrong).

I guess the infinitive form is a bit more literary (although this is very subjective), which is less suitable in a context of technical documentation, and that's why I chose the gerund form in my commit.

Obviously, I'd be willing to commit again with the infinitive form if it's considered a better fit.