Fix staticcheck QF1001: apply De Morgan's law in isFullSHA

Author: joshfriend

cmd/gradle-cache/main.go

@@ -836,7 +836,7 @@ func isFullSHA(s string) bool {
 		return false
 	}
 	for _, c := range s {
-		if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f')) {
+		if (c < '0' || c > '9') && (c < 'a' || c > 'f') {
 			return false
 		}
 	}