dnsdist-1.9.x: Update the Rust version we use in our packages to 1.78

[rgacogne]

Short description

The boring-sys crate used by Quiche uses a version of the bindgen crate that requires Rust >= 1.77.0.

We already upgraded the Rust version in the default branch in #14252

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)
• checked that this code was merged to master

[coveralls]

Pull Request Test Coverage Report for Build 10956272316

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 8 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.006%) to 55.741%

---

Files with Coverage Reduction	New Missed Lines	%
pdns/dnsdistdist/dnsdist-async.cc	2	82.21%
pdns/dnsdist-carbon.cc	6	59.89%

Totals
Change from base Build 10789900067:	-0.006%
Covered Lines:	47996
Relevant Lines:	65546

---

💛 - Coveralls