chore: GitHub action and swiftlint cleanup

[drmohundro]

Includes:

• bump in github swiftlint action version
• run github actions on push and pull_request
• prefer implicit return fix for swiftlint

[codecov]

Codecov Report

Merging #231 into master will not change coverage.
The diff coverage is 70.21%.

@@           Coverage Diff           @@
##           master     #231   +/-   ##
=======================================
  Coverage   74.98%   74.98%           
=======================================
  Files          13       13           
  Lines        1851     1851           
=======================================
  Hits         1388     1388           
  Misses        463      463

Impacted Files	Coverage Δ
Tests/SWXMLHashTests/SWXMLHashConfigTests.swift	63.63% <0%> (ø)	⬆️
...ests/SWXMLHashTests/LazyTypesConversionTests.swift	71.87% <0%> (ø)	⬆️
Tests/SWXMLHashTests/LazyXMLParsingTests.swift	76.92% <0%> (ø)	⬆️
...SWXMLHashTests/MixedTextWithXMLElementsTests.swift	60% <0%> (ø)	⬆️
.../TypeConversionArrayOfNonPrimitiveTypesTests.swift	70.22% <0%> (ø)	⬆️
...ts/SWXMLHashTests/LazyWhiteSpaceParsingTests.swift	76.19% <0%> (ø)	⬆️
Tests/SWXMLHashTests/XMLParsingTests.swift	85.38% <0%> (ø)	⬆️
Tests/SWXMLHashTests/WhiteSpaceParsingTests.swift	75% <0%> (ø)	⬆️
...LHashTests/TypeConversionPrimitypeTypesTests.swift	67.39% <0%> (ø)	⬆️
...XMLHashTests/TypeConversionComplexTypesTests.swift	66.66% <66.66%> (ø)	⬆️
... and 3 more

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