Release v1.6.2 changes

• Versions are bumped to 1.6.2 for crates and 1620 for runtime (#4281).

This release is intended to fix a few issues appeared with publishing previous v1.6.1, also implementing small fixes.
Runtimes are the same with v1.6.1 and v1.6.0.

• Gear tooling that run wasms now uses Wasmer instead of Wasmi as underlying executor (#4261);
• Fixed gtest v1.6.1 bug caused user space panic for some rare cases (#4270);
• gstd now uses waker-fn crate instead of custom waker for async runtime (#4271);
• Fixed gstd documentation publishing caused by inclusion of ethexe feature (#4278).

Full Changelog: v1.6.1...v1.6.2