Use base actions image for rustfmt check (#241)

The `timescaledev/rust-builder` is outdated, and we don't need it
anyways because everything in it we need is in the base GH Actions
image. This fixes the CI failure in #240 stemming from this action's
Docker image using an outdated Rust compiler.

It also speeds up the check significantly, because we don't need to wait
for the Docker image to be setup anymore.

Author: syvb

.github/workflows/code_checks.yml

@@ -7,9 +7,6 @@ jobs:
   fmt:
     runs-on: ubuntu-latest
 
-    container:
-      image: timescaledev/rust-builder:ubuntu-1.65
-
     steps:
       - name: Checkout
         uses: actions/checkout@v4