Auto merge of #91715 - the8472:bump-rmeta-fromat-version, r=Mark-Simulacrum

Bump rmeta version to fix rustc_serialize ICE

#91407 changed the serialization format which leads to ICEs for nightly users such as #91663 and linked issues. The issue can be solved by running `cargo clean`. But bumping the metadata version should lead to the cached files being discarded, avoiding the issue entirely.

Author: bors

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -48,7 +48,7 @@ crate fn rustc_version() -> String {
 /// Metadata encoding version.
 /// N.B., increment this if you change the format of metadata such that
 /// the rustc version can't be found to compare with `rustc_version()`.
-const METADATA_VERSION: u8 = 5;
+const METADATA_VERSION: u8 = 6;
 
 /// Metadata header which includes `METADATA_VERSION`.
 ///