ci: Specify x86_64-unknown-uefi for clippy

Use the correct target for clippy as unwind features and symbols are no
longer used in redox_uefi_std. Fixes:

    error: unwinding panics are not supported without std

Signed-off-by: Tim Crawford <tcrawford@system76.com>

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ on:
 
 jobs:
   lint:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
     - uses: actions/checkout@v4
 
@@ -16,10 +16,11 @@ jobs:
     - name: clippy
       env:
         BASEDIR: "."
-      run: cargo clippy
+      run: cargo clippy --target x86_64-unknown-uefi -- -D warnings
+      continue-on-error: true
 
   build:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
     - uses: actions/checkout@v4