Pin proc-macro2 in CI to fix MSRV breakage

The proc-macro2 crate switched to Rust edition 2021 starting with
v1.0.66, i.e., has MSRV of 1.56.

Here, we pin it in CI to fix the breakage.

Author: tnull

ci/ci-tests.sh

@@ -30,6 +30,12 @@ popd
 # The addr2line v0.20 crate (a dependency of `backtrace` starting with 0.3.68) relies on 1.55+
 [ "$RUSTC_MINOR_VERSION" -lt 55 ] && cargo update -p backtrace --precise "0.3.67" --verbose
 
+# The quote crate switched to Rust edition 2021 starting with v1.0.31, i.e., has MSRV of 1.56
+[ "$RUSTC_MINOR_VERSION" -lt 56 ] && cargo update -p quote --precise "1.0.30" --verbose
+
+# The proc-macro2 crate switched to Rust edition 2021 starting with v1.0.66, i.e., has MSRV of 1.56
+[ "$RUSTC_MINOR_VERSION" -lt 56 ] && cargo update -p proc-macro2 --precise "1.0.65" --verbose
+
 # The serde_json crate switched to Rust edition 2021 starting with v1.0.101, i.e., has MSRV of 1.56
 [ "$RUSTC_MINOR_VERSION" -lt 56 ] && cargo update -p serde_json --precise "1.0.100" --verbose