Add GitHub Actions for Tests, Lint

[petergoldstein]

To support the range of Ruby 2.6-3.1 in CI, this change also adds a development dependence on activesupport locked to ~> 6.1

[guardrails]

⚠️ We detected 7 security issues in this pull request:

Vulnerable Libraries (7)

Severity	Details
Medium	pkg:gem/activesupport@6.1.4.4@6.1.4.4 - no patch available
Critical	pkg:gem/jmespath@1.5.0@1.5.0 - no patch available
N/A	pkg:gem/nokogiri@1.13.1@1.13.1 upgrade to: 1.13.2
High	pkg:gem/i18n@1.8.11@1.8.11 - no patch available
High	pkg:gem/rack@2.2.3@2.2.3 - no patch available
N/A	activesupport@6.1.4.4 upgrade to: '> 5.2.8, >= 5.2.8.15', '> 6.1.7, >= 6.1.7.1', '>= 7.0.4.1'
N/A	jmespath@6.1.4.4 upgrade to: '> 5.2.8, >= 5.2.8.15', '> 6.1.7, >= 6.1.7.1', '>= 7.0.4.1'

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