chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/firewall/iptables/list_test.go

@@ -13,30 +13,25 @@ func Test_parseChain(t *testing.T) {
 	testCases := map[string]struct {
 		iptablesOutput string
 		table          chain
-		errWrapped     error
 		errMessage     string
 	}{
 		"no_output": {
-			errWrapped: ErrChainListMalformed,
 			errMessage: "iptables chain list output is malformed: not enough lines to process in: ",
 		},
 		"single_line_only": {
 			iptablesOutput: `Chain INPUT (policy ACCEPT 140K packets, 226M bytes)`,
-			errWrapped:     ErrChainListMalformed,
 			errMessage: "iptables chain list output is malformed: not enough lines to process in: " +
 				"Chain INPUT (policy ACCEPT 140K packets, 226M bytes)",
 		},
 		"malformed_general_data_line": {
 			iptablesOutput: `Chain INPUT
 num pkts bytes target     prot opt in     out     source               destination`,
-			errWrapped: ErrChainListMalformed,
 			errMessage: "parsing chain general data line: iptables chain list output is malformed: " +
 				"expected 8 fields in \"Chain INPUT\"",
 		},
 		"malformed_legend": {
 			iptablesOutput: `Chain INPUT (policy ACCEPT 140K packets, 226M bytes)
 num pkts bytes target     prot opt in     out     source`,
-			errWrapped: ErrChainListMalformed,
 			errMessage: "iptables chain list output is malformed: legend " +
 				"\"num pkts bytes target     prot opt in     out     source\" " +
 				"is not the expected \"num pkts bytes target prot opt in out source destination\"",
@@ -135,9 +130,10 @@ num pkts bytes target     prot opt in     out     source               destinati
 			table, err := parseChain(testCase.iptablesOutput)
 
 			assert.Equal(t, testCase.table, table)
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 		})
 	}