Make sketch filename matching rule case-sensitive

[per1234]

The primary sketch file name must match the sketch folder exactly. Previously, the sketch file name matching rule (SS001) did not check for file name case matching on case-insensitive file systems.

[codecov-io]

Codecov Report

Merging #162 (1f72538) into main (9477e68) will increase coverage by 0.00%.
The diff coverage is 71.42%.

@@           Coverage Diff           @@
##             main     #162   +/-   ##
=======================================
  Coverage   84.26%   84.27%           
=======================================
  Files          43       43           
  Lines        2956     2957    +1     
=======================================
+ Hits         2491     2492    +1     
  Misses        373      373           
  Partials       92       92           

Flag	Coverage Δ
unit	84.27% <71.42%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/rule/rulefunction/sketch.go	92.59% <71.42%> (+0.13%)	⬆️

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[per1234]

I had to make 83c70fd in order to make the "Check for forgotten code generation" step of the "Run tests" workflow pass (https://github.com/per1234/arduino-lint/runs/1918271782?check_suite_focus=true#step:6:15), but this is not in any way related to the code changes made in this PR.