Rollup merge of #7239 - flip1995:ci-windows-rustup, r=flip1995

CI: update rustup before installing the toolchain on windows

Ok, fine windows, if this is what you want, take it...

r? `@ghost`

changelog: none

.github/workflows/clippy_bors.yml

@@ -90,6 +90,11 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v2.3.3
 
+    # FIXME: should not be necessary once 1.24.2 is the default version on the windows runner
+    - name: Update rustup
+      run: rustup self update
+      if: runner.os == 'Windows'
+
     - name: Install toolchain
       run: rustup show active-toolchain