test: fix the stale default disc paths -- three tests could never run unaided

texture_disc.rs and mesh_disc.rs fall back to "/home/fabi/RE Project Sylpheed/..."
when SYLPHEED_ISO / SYLPHEED_RES3D are unset. The directory is "RE - Project
Sylpheed"; the fallbacks were missing the " - ", so stage_models_decode,
stage_models_sweep and stage_models_quality_audit failed with NotFound for anyone
who did not happen to know the env var. They now pass unaided (10/10 in
mesh_disc).

Found while auditing what the suite actually exercises after withdrawing the
anchor change: an ISO-gated test skipping, and an ignored test failing on a typo,
are both "green" in a normal run.

Full state, with SYLPHEED_ISO/DISC/RES3D set and --include-ignored: 82 lib tests
and every disc/ISO suite pass; the single failure is
shared_resources_decode_identically_in_every_container, which is deliberately
written as the target state and #[ignore]d.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/sylpheed-formats/tests/texture_disc.rs

@@ -19,7 +19,7 @@ fn iso_path() -> Option<PathBuf> {
         }
     }
     let default = PathBuf::from(
-        "/home/fabi/RE Project Sylpheed/Project Sylpheed - Arc of Deception (USA, Europe) (En,Ja).iso",
+        "/home/fabi/RE - Project Sylpheed/Project Sylpheed - Arc of Deception (USA, Europe) (En,Ja).iso",
     );
     default.is_file().then_some(default)
 }