Update MPFR to 4.2.2

[eschnett]

Julia's direct dependency MPFR should be updated to 4.2.2.

This could be backported to the 1.12 release branch.

[nsajko]

The formatted output functions behave incorrectly with %c on the value 0. Such a use is uncommon, but this bug may have security implications.
Corresponding changesets in the 4.2 branch: 6061dcfbb, 154c11b26.