Bump org.bouncycastle:bcprov-jdk15to18 from 1.72 to 1.78.1

[Njko]

Is your feature request related to a problem? Please describe.
The dependency to bouncycastle is reported to be obsolete and potentially vulnerable.

Describe the solution you'd like
Update the dependency org.bouncycastle:bcprov-jdk15to18 to the version 1.78.1 (as time of writing issue)

Check the type of feature request:

• Feature available in a newer PDFBox desktop version
• Feature not yet ported to PdfBox-Android
• Other

Additional context
It appears that Dependabot is not working for 6 months now