perf: avoid allocations with `(*regexp.Regexp).MatchString` (#1283)

We should use `(*regexp.Regexp).MatchString` instead of
`(*regexp.Regexp).Match([]byte(...))` when matching string to avoid
unnecessary `[]byte` conversions and reduce allocations.

Example benchmark:

var pathRegex = regexp.MustCompile(".*.yaml")

func BenchmarkMatch(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := pathRegex.Match([]byte("./config/deploy.yaml")); !match {
			b.Fail()
		}
	}
}

func BenchmarkMatchString(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := pathRegex.MatchString("./config/deploy.yaml"); !match {
			b.Fail()
		}
	}
}

goos: linux
goarch: amd64
pkg: github.com/zricethezav/gitleaks/v8/detect
cpu: AMD Ryzen 7 PRO 4750U with Radeon Graphics
BenchmarkMatch-16          	 2167712	       657.9 ns/op	      24 B/op	       1 allocs/op
BenchmarkMatchString-16    	 3275372	       324.8 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/zricethezav/gitleaks/v8/detect	3.436s

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

detect/detect.go

@@ -220,7 +220,7 @@ func (d *Detector) detectRule(fragment Fragment, rule config.Rule) []report.Find
 
 	if rule.Path != nil && rule.Regex == nil {
 		// Path _only_ rule
-		if rule.Path.Match([]byte(fragment.FilePath)) {
+		if rule.Path.MatchString(fragment.FilePath) {
 			finding := report.Finding{
 				Description: rule.Description,
 				File:        fragment.FilePath,
@@ -235,7 +235,7 @@ func (d *Detector) detectRule(fragment Fragment, rule config.Rule) []report.Find
 		// if path is set _and_ a regex is set, then we need to check both
 		// so if the path does not match, then we should return early and not
 		// consider the regex
-		if !rule.Path.Match([]byte(fragment.FilePath)) {
+		if !rule.Path.MatchString(fragment.FilePath) {
 			return findings
 		}
 	}