build(deps): bump github.com/urfave/cli/v2 from 2.25.7 to 2.26.0

Bumps [github.com/urfave/cli/v2](https://github.com/urfave/cli) from 2.25.7 to 2.26.0.
- [Release notes](https://github.com/urfave/cli/releases)
- [Changelog](https://github.com/urfave/cli/blob/main/docs/CHANGELOG.md)
- [Commits](https://github.com/urfave/cli/compare/v2.25.7...v2.26.0)

---
updated-dependencies:
- dependency-name: github.com/urfave/cli/v2
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/github.com/urfave/cli/v2/flag_timestamp.go

@@ -120,8 +120,13 @@ func (f *TimestampFlag) GetDefaultText() string {
 	if f.DefaultText != "" {
 		return f.DefaultText
 	}
-	if f.defaultValue != nil && f.defaultValue.timestamp != nil {
-		return f.defaultValue.timestamp.String()
+	val := f.Value
+	if f.defaultValueSet {
+		val = f.defaultValue
+	}
+
+	if val != nil && val.timestamp != nil {
+		return val.timestamp.String()
 	}
 
 	return ""
@@ -144,6 +149,7 @@ func (f *TimestampFlag) Apply(set *flag.FlagSet) error {
 	f.Value.SetLocation(f.Timezone)
 
 	f.defaultValue = f.Value.clone()
+	f.defaultValueSet = true
 
 	if val, source, found := flagFromEnvOrFile(f.EnvVars, f.FilePath); found {
 		if err := f.Value.Set(val); err != nil {