tor-config: Rename to ReconfigureError::UnsupportedSituation

From Unsupported.  Prompted by
  https://gitlab.torproject.org/tpo/core/arti/-/merge_requests/889#note_2856873
This was added in this MR.

Also add the missing semver note.

crates/tor-config/semver.md

@@ -1 +1,2 @@
 ADDED: ConfigBuildError::NoCompileTimeSupport
+ADDED: ReconfigureError::UnsupportedSituation

crates/tor-config/src/err.rs

@@ -117,7 +117,7 @@ pub enum ReconfigureError {
     /// by this build of arti -
     /// that should be reported at config build type as `ConfigBuildError::Unsupported`.
     #[error("Configuration not supported in this situation: {0}")]
-    Unsupported(String),
+    UnsupportedSituation(String),
 
     /// There was a programming error somewhere in our code, or the calling code.
     #[error("Programming error")]

crates/tor-guardmgr/src/err.rs

@@ -163,7 +163,7 @@ impl From<GuardMgrConfigError> for tor_config::ReconfigureError {
         use tor_config::ReconfigureError as R;
         use GuardMgrConfigError as G;
         match g {
-            e @ G::NoLock(_) => R::Unsupported(e.to_string()),
+            e @ G::NoLock(_) => R::UnsupportedSituation(e.to_string()),
         }
     }
 }