Fix CI

[jayvdb]

CI broke on main https://github.com/Electron100/butane/actions/runs/8401909942/job/23019123599
while it was green at #221

error: fields `id`, `title`, and `pub_time` are never read
Error:   --> butane/tests/common/blog.rs:73:9
   |
72 | pub struct PostMetadata {
   |            ------------ fields in this struct
73 |     pub id: i64,
   |         ^^
74 |     pub title: String,
   |         ^^^^^
75 |     #[cfg(feature = "datetime")]
76 |     pub pub_time: Option<NaiveDateTime>,
   |         ^^^^^^^^
   |
   = note: `-D dead-code` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(dead_code)]`

error: could not compile `butane` (test "fake") due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: field `pub_time` is never read
Error:   --> butane/tests/common/blog.rs:76:9
   |
[72](https://github.com/jayvdb/butane/actions/runs/8405991704/job/23019393419#step:15:73) | pub struct PostMetadata {
   |            ------------ field in this struct
...
76 |     pub pub_time: Option<NaiveDateTime>,
   |         ^^^^^^^^
   |
   = note: `-D dead-code` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(dead_code)]`

error: could not compile `butane` (test "query") due to 1 previous error
Error: Process completed with exit code 101.

I'm not sure why, but this appears to fix it. I suspect the default rust on these images is a bit old.