refactor(get-modflow): use Path.replace instead of Path.rename

[wpbonelli]

The behavior of Path.rename() is inconsistent between platforms: on Windows an error is raised if a file with the new name already exists, while on Linux and macOS the file is silently replaced. This PR updates get-modflow to use Path.replace() instead of Path.rename() when moving binaries from the download directory to bin directory, for consistent behavior.

One case for which this is relevant is installing a full suite of binaries from the executables distribution, plus bleeding-edge versions of mf6, mf5to6, mf2005, and zbud6 from the modflow6-nightly-build distribution. An easy way to do this is running get-modflow twice, e.g.

get-modflow bin
get-modflow bin --repo modflow6-nightly-build

Currently this works on macOS and Linux but not on Windows.

[codecov]

Codecov Report

Merging #1822 (e7804c0) into develop (63ea5fc) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##           develop   #1822   +/-   ##
=======================================
  Coverage     72.0%   72.0%           
=======================================
  Files          255     255           
  Lines        57369   57363    -6     
=======================================
- Hits         41340   41336    -4     
+ Misses       16029   16027    -2     

Impacted Files	Coverage Δ
flopy/utils/get_modflow.py	64.1% <100.0%> (ø)

... and 2 files with indirect coverage changes