Update libs.versions.toml

[camille-banyan]

Resolve illegal reflective access warnings (#314) by downgrading the retrofit version from 2.9.0 to 2.7.2. After I did this locally, the warnings went away which was noted in #62.

[cryptoapebot]

I think the other option is to use gradle 8.0.2 or 8.1.1

PS F:\workspace\openai-java> gradle --version

------------------------------------------------------------
Gradle 8.0.2
------------------------------------------------------------

Build time:   2023-03-03 16:41:37 UTC
Revision:     7d6581558e226a580d91d399f7dfb9e3095c2b1d

Kotlin:       1.8.10
Groovy:       3.0.13
Ant:          Apache Ant(TM) version 1.10.11 compiled on July 10 2021
JVM:          19.0.2 (Oracle Corporation 19.0.2+7-44)
OS:           Windows 10 10.0 amd64

PS F:\workspace\openai-java>