anchor: Use Rust 1.79

Building with Rust 1.80 fails with:

```
 error[E0282]: type annotations needed for `Box<_>`
  --> /Users/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/time-0.3.29/src/format_description/parse/mod.rs:83:9
   |
83 |     let items = format_items
   |         ^^^^^
...
86 |     Ok(items.into())
   |              ---- type must be known at this point
   |
help: consider giving `items` an explicit type, where the placeholders `_` are specified
   |
83 |     let items: Box<_> = format_items
   |              ++++++++
```

.github/workflows/anchor.yml

@@ -48,7 +48,7 @@ jobs:
       - name: Install Rust toolchain
         uses: actions-rs/toolchain@v1
         with:
-          toolchain: stable
+          toolchain: 1.79
           override: true
 
       # Why gcc-multilib? blake3 crate expects bits/wordsize.h header...
@@ -84,10 +84,6 @@ jobs:
         run: |
           cargo build --package anchor-cli --release --target ${{ matrix.target }}
 
-      - name: Setup tmate session
-        if: ${{ failure() }}
-        uses: mxschmitt/action-tmate@v3
-
       - name: Copy binary
         run: |
           cp target/${{ matrix.target }}/release/anchor anchor-${{ matrix.suffix }}