Bump LibCURL to 7.78.0

[bluesmoon]

This is a followup to JuliaPackaging/Yggdrasil#3575
bumping LibCURL in stdlibs as well.

[DilumAluthge]

You'll need to:

1. Delete the old checksums.
2. Add the new checksums.
3. Use contrib/refresh_checksums.mk to correctly pack the checksums into the appropriate files.

[staticfloat]

Note that steps 2 and 3 are both done by running contrib/refresh_checksums.mk.

[bluesmoon]

Ok, that's going to be hard to do since I don't have julia checked out locally. I'm making the changes via the github web UI. I use Julia 1.5 locally which does not have LibCURL built into stdlib.

[staticfloat]

I did it for you.

[bluesmoon]

Thank you :)

[StefanKarpinski]

Thank you guys for doing this!

[ViralBShah]

We are now on 7.81.