Fix CI bootstrap build with a nightly rust compiler

The CI failed to compile some recent code that requires a nightly
feature. This change allows the CI to use a nightly compiler instead.

ChangeLog:

	* .github/workflows/bootstrap.yml: Install nightly rustc.

Signed-off-by: Pierre-Emmanuel Patry <[email protected]>

Author: P-E-P

.github/workflows/bootstrap.yml

@@ -29,6 +29,7 @@ jobs:
                   gcc-multilib \
                   g++-multilib \
                   dejagnu
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --default-toolchain=nightly;
 
     - name: Configure
       run: |