Don't run nightly on CI (#870)

* Exclude sqlx example

Getting an ICE
https://github.com/tokio-rs/axum/runs/5602144413?check_suite_focus=true.
Will look into that later.

* actually it was nightly's fault

* and don't test things on nightly

.github/workflows/CI.yml

@@ -17,7 +17,7 @@ jobs:
     - uses: actions/checkout@master
     - uses: actions-rs/toolchain@v1
       with:
-        toolchain: nightly
+        toolchain: beta
         override: true
         profile: minimal
         components: clippy, rustfmt
@@ -69,7 +69,9 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust: [stable, beta, nightly]
+        # nightly has an ICE, so ignore it for now
+        # rust: [stable, beta, nightly]
+        rust: [stable, beta]
     steps:
     - uses: actions/checkout@master
     - uses: actions-rs/toolchain@v1