Avoid allocations with (*regexp.Regexp).MatchString

[Juneezee]

We should use (*regexp.Regexp).MatchString instead of (*regexp.Regexp).Match([]byte(...)) when matching string to avoid unnecessary []byte conversions and reduce allocations. A one-line change for free performance improvement.

Example benchmark:

var defaultTagRegex = regexp.MustCompile("\n *#nosec")

func BenchmarkMatch(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := defaultTagRegex.Match([]byte("\n #nosec")); !match {
			b.Fail()
		}
	}
}

func BenchmarkMatchString(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := defaultTagRegex.MatchString("\n #nosec"); !match {
			b.Fail()
		}
	}
}

Result:

goos: linux
goarch: amd64
pkg: github.com/securego/gosec/v2
cpu: AMD Ryzen 7 PRO 4750U with Radeon Graphics
BenchmarkMatch-16          	 5367033	       210.6 ns/op	       8 B/op	       1 allocs/op
BenchmarkMatchString-16    	 9321561	       126.3 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/securego/gosec/v2	3.606s

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (64bbe90) 72.32% compared to head (5ee005f) 72.32%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1062   +/-   ##
=======================================
  Coverage   72.32%   72.32%           
=======================================
  Files          50       50           
  Lines        3447     3447           
=======================================
  Hits         2493     2493           
  Misses        880      880           
  Partials       74       74           

Files	Coverage Δ
analyzer.go	85.87% <100.00%> (ø)

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