fix(backend): build packslip after versions_host_applies was removed

#14459 replaced `versions_host_applies()` with `versions_host_tool()`,
while #14466 added two new calls to the old method. The two merged
independently, so main no longer compiles. Use
`versions_host_tool().is_some()`, which is what the old method meant.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Entire-Checkpoint: 01M4YAFDYQ89A14EKJTW2DNYGC

src/backend/packslip.rs

@@ -1318,7 +1318,7 @@ impl PackslipBackend {
         let Some(repo) = Self::repo(project) else {
             return Ok(None);
         };
-        if !self.versions_host_applies() {
+        if self.versions_host_tool().is_none() {
             return Ok(None);
         }
         let tag = |versions: &[VersionInfo]| {
@@ -1350,7 +1350,7 @@ impl PackslipBackend {
     ) -> Result<Vec<VersionInfo>> {
         // A listing from the versions host lags GitHub, so it is not reused
         // once the host is turned off.
-        let context = if self.versions_host_applies() {
+        let context = if self.versions_host_tool().is_some() {
             "packslip-vendor-listing"
         } else {
             "packslip-vendor-listing-direct"