The 2 tests need fixing:
The first one is trivial, the expectation can be changed to 59 due to the new rule (maybe we can add some better logic to automatically determine the number of total rules to avoid having to update this test every time...):
[-] get Rules with no parameters supplied 60ms
Expected 58, but got 59.
74: $defaultRules.Count | Should -Be $expectedNumRules
at , C:\projects\psscriptanalyzer\Tests\Engine\GetScriptAnalyzerRule.tests.ps1: line 74
[+] is a positional parameter 14ms
Context When used incorrectly

The second test is for the documentation to have a matching rule document for every rule. Somehow it does not find the PSAvoidLongLines rules. It uses Get-ScriptAnalyzerRule for that, check if the rule gets returned here or maybe it is simply missing the PS prefix in the name?

[-] Every rule must have an entry in the rule documentation README.md file 26ms
Expected $null or empty, but got PSAvoidLongLines.
46: $rulesReadmeDiff | Where-Object SideIndicator -eq "<=" | Foreach-Object InputObject | Should -BeNullOrEmpty
at , C:\projects\psscriptanalyzer\Tests\Documentation\RuleDocumentation.tests.ps1: line 46