Proper C-style formatting for integer

[DimitriPapadopoulos]

Variable port is initialized as an integer, should be formatted with %d.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

Merging #913 (d364fff) into master (1711b16) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #913   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          32       32           
  Lines       11216    11216           
=======================================
  Hits        11210    11210           
  Misses          6        6           

Impacted Files	Coverage Δ
zarr/tests/test_storage.py	100.00% <100.00%> (ø)