Fix support for Go < 1.21

Technically I'm fixing it at the same time that I'm removing the tests
in the pipeline that would have caught this. Version support lower than
the last 3 minor versions is definitely not a priority, and only
something I'm fixing here because it's absolutely trivial.

.github/workflows/test.yml

@@ -18,9 +18,9 @@ jobs:
           - ubuntu-latest
           - windows-latest
         go-version:
-          - '1.20'
           - '1.21'
           - '1.22'
+          - '1.23'
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v3
@@ -43,7 +43,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v4
         with:
-          go-version: '1.22'
+          go-version: '1.23'
       - name: Lint
         uses: golangci/golangci-lint-action@v3
         with:

internal/jsondiff/jsondiff.go

@@ -6,7 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"reflect"
-	"slices"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -149,7 +149,7 @@ func (d *differ) diffMaps(got, want map[string]any) {
 	for k := range keys {
 		sortedKeys = append(sortedKeys, k)
 	}
-	slices.Sort(sortedKeys)
+	sort.Strings(sortedKeys)
 
 	first := true
 	for _, k := range sortedKeys {
@@ -300,7 +300,7 @@ func (d *differ) writeMap(m map[string]any) {
 	for k := range m {
 		keys = append(keys, k)
 	}
-	slices.Sort(keys)
+	sort.Strings(keys)
 
 	first := true
 	for _, k := range keys {