Tested compilers list up to date?

On https://www.boost.org/releases/latest/ is written:

```
Boost’s primary test compilers are:
Linux:
Clang, C++03: 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 12.0.0, 13.0.0, 14.0.0, 15.0.0
Clang, C++11: 3.4, 11.0.0, 13.0.0, 14.0.0, 15.0.0
Clang, C++14: 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 5.0, 12.0.0, 13.0.0, 14.0.0, 15.0.0
Clang, C++17: 6.0.1, 7.0.0, 8.0.0, 9.0.0, 10.0.0, 11.0.0, 12.0.0, 13.0.0, 14.0.0, 15.0.0
Clang, C++20: 11.0.0, 12.0.0, 13.0.0, 14.0.0, 15.0.0
GCC, C++03: 4.6.3, 11, 12
GCC, C++11: 4.7.3, 4.8.5, 11, 12
GCC, C++14: 5.4.0, 6.4.0, 7.3.0, 8.0.1, 9.1.0, 11, 12
GCC, C++17: 7.3.0, 8.0.1, 9.1.0, 11, 12
GCC, C++20: 8.0.1, 9.1.0, 10, 11, 12
```

This compiler versions seem quiet old. Is this list correct?

Start at the latest-release page linked in the issue and verify the listed primary Clang and GCC versions against the current tested compiler matrix. Done means the page accurately reflects the versions that Boost currently tests, with outdated entries removed or current entries added.

Written by the indexing model from the issue text.