Switch to using -Z direct-minimal-versions

So far we have relied on the unstable -Z minimal-versions switch to the
cargo update command in order to downgrade all dependencies to their
minimum supported versions to ensure that our own documented minimum
supported Rust version is kosher.
This option is unlikely to ever be stabilized in this form and a more
promising candidate is what is now available with -Z
direct-minimal-versions. This option only downgrades the direct
dependencies of the crate, which should still be sufficient for our
intents and purposes and is less likely to have runtime related
performance problems. Switch to using it instead of -Z minimal-versions.

.github/workflows/test.yml

@@ -54,7 +54,7 @@ jobs:
         with:
           profile: minimal
           toolchain: nightly
-      - run: cargo +nightly -Z minimal-versions update
+      - run: cargo +nightly -Z direct-minimal-versions update
       - name: Install minimum Rust
         uses: actions-rs/toolchain@v1
         with:

Cargo.toml

@@ -36,8 +36,8 @@ trace = []
 log = []
 
 [dependencies]
-proc-macro2 = {version = "1.0.32", default-features = false}
-quote = {version = "1.0", default-features = false}
+proc-macro2 = {version = "1.0.60", default-features = false}
+quote = {version = "1.0.25", default-features = false}
 syn = {version = "2.0", default-features = false, features = ["full", "parsing", "printing", "proc-macro"]}
 
 [dev-dependencies]