Three lint violations in test files were causing the CI Lint job to fail on every push to main.

Fixes

• errorlint (module_test.go:894): Replace direct type assertion err.(*ParseError) with errors.As — direct assertions break on wrapped errors
• errcheck (module_test.go:1032): Handle the ignored error return from filepath.Abs
• staticcheck SA9003 (cgen_test.go:2380): Remove empty if !checker.Check(program) branch; call directly

// before
if _, ok := err.(*ParseError); !ok { ... }
absDir, _ := filepath.Abs(tmpDir)
if !checker.Check(program) { /* comment */ }

// after
var parseErr *ParseError
if !errors.As(err, &parseErr) { ... }
absDir, err := filepath.Abs(tmpDir)
if err != nil { t.Fatalf(...) }
checker.Check(program)

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