internal/plugin: remove zero-width spaces from plugin name comment

The comment describing allowed plugin name characters contained three
U+200B (zero-width space) characters around the '_' and '-' literals.
The rendered comment is identical without them; the ZWSP were likely
copy-pasted from a rich-text source.

Downstream impact: every project that vendors helm.sh/helm/v4 and runs
Renovate gets a repo-wide warning on its Dependency Dashboard about
hidden Unicode characters. Renovate scans the whole tree (including
vendor/) for ZWSP/bidi-override codepoints and cannot be told to skip
a path for this specific check. Removing the characters here clears
the warning everywhere downstream.

Signed-off-by: Aleksei Sviridkin <f@lex.la>

internal/plugin/plugin.go

@@ -77,5 +77,5 @@ type Output struct {
 
 // validPluginName is a regular expression that validates plugin names.
 //
-// Plugin names can only contain the ASCII characters a-z, A-Z, 0-9, ​_​ and ​-.
+// Plugin names can only contain the ASCII characters a-z, A-Z, 0-9, _ and -.
 var validPluginName = regexp.MustCompile("^[A-Za-z0-9_-]+$")