Address a code TODO about error message in `RequiredPackageVariableSource`

[m1kola]

It looks like this can be addressed now since I believe version ranges already landed in main:

operator-controller/internal/resolution/variablesources/required_package.go

Lines 93 to 108 in c24fdbc

	func (r *RequiredPackageVariableSource) notFoundError() error {
	// TODO: update this error message when/if we decide to support version ranges as opposed to fixing the version
	// context: we originally wanted to support version ranges and take the highest version that satisfies the range
	// during the upstream call on the 2023-04-11 we decided to pin the version instead. But, we'll keep version range
	// support under the covers in case we decide to pivot back.
	if r.versionRange != "" && r.channelName != "" {
	return fmt.Errorf("package '%s' at version '%s' in channel '%s' not found", r.packageName, r.versionRange, r.channelName)
	}
	if r.versionRange != "" {
	return fmt.Errorf("package '%s' at version '%s' not found", r.packageName, r.versionRange)
	}
	if r.channelName != "" {
	return fmt.Errorf("package '%s' in channel '%s' not found", r.packageName, r.channelName)
	}
	return fmt.Errorf("package '%s' not found", r.packageName)
	}