Test with Swift 5.6 Linux in CI

[marcelofabri]

No description provided.

[codecov-commenter]

Codecov Report

Merging #3902 (ec9c539) into master (ca2712a) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3902   +/-   ##
=======================================
  Coverage   92.60%   92.60%           
=======================================
  Files         436      436           
  Lines       21964    21964           
=======================================
+ Hits        20339    20340    +1     
+ Misses       1625     1624    -1     

Impacted Files	Coverage Δ
...iftLintFramework/Extensions/String+SwiftLint.swift	90.90% <0.00%> (+1.51%)	⬆️

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[marcelofabri]

Interesting, most (all?) the failures seem to be related to SwiftLint commands tests (using swiftlint:disable & friends). Maybe a regression from #3872?

Or do we need to update SwiftSyntax before being able to compile/run the tests in a new Swift version now?

[jpsim]

See #3901