SFT-3537: Remove proc-macro2 pin from CI.

* .github/workflows/dependencies.yaml (are-versions-really-minimal):
Remove cargo pin for proc-macro2.

.github/workflows/dependencies.yaml

@@ -29,13 +29,4 @@ jobs:
         with:
           toolchain: nightly
       - run: rustup override set nightly
-      # proc-macro2 is broken in recent nightly versions of Rust as it
-      # automagically enables some nightly features that don't exist on recent
-      # nightly compilers.
-      #
-      # Once our dependencies update the proc-macro2 version used to be higher
-      # than the one pinned here we can remove this hack.
-      #
-      # This is not needed for stable versions.
-      - run: cargo update -p proc-macro2 --precise 1.0.66 -Z minimal-versions
       - run: cargo check -Z minimal-versions