Rollup merge of #78853 - calebcartwright:fix-const-block-expr-span, r=spastorino

rustc_parse: fix ConstBlock expr span

The span for a ConstBlock expression should presumably run through the end of the block it contains and not stop at the keyword, just like is done with similar block-containing expression kinds, such as a TryBlock

diff --cc compiler/rustc_parse/src/parser/mod.rs
Simple merge