Trivial: Upgrade remaining actions/checkout to v4 ...

Avoid deprecated Node 16.

Upgrade checkout and codecov to latest version ...

Get rid of a deprecation message about Node 16.

Add a CI step to upload assets on release creation ...

We haven't had assets generated for releases since v1.29.0,
however some external code depend on them (dlang-community/setup-dlang, namely).
This will fix it and make it less likely to be forgotten in the future.

Build the tests and binary with -cov on POSIX ...

The CI was sending empty coverage reports because nothing
was being generated, as the variable was always false.
In the process, a bit of dead code was removed.

CI: Move single checks to Github, remove dead code ...

Remove support for very old frontend - we were not testing it anyways.
Move the useful checks to another job so they run once.

Remove internal mentions to Travis

Re-add CodeCov support

Update supported compiler versions ...

This is to support using `-preview=in` and reducing
the amount of deprecations.

CI: Re-enable LDC master

improve github CI definitions ...

- skip CI on changes only to changelog/
- reduce permissions of GH token for PR comment

CI: Exclude some tests with DMD on Windows

CI: Enable test/run-unittest.sh on Windows

fix pr_info_post file paths

try to fix pr_info permission problem (#2621) ...

* try to fix pr_info permissions problem

* new safer pr_info

add pr_info GitHub actions run ...

Gives summary about some basic statistics, deprecations and warnings

reintroduce dmd-latest to CI runner ...

close #2199

CI: Add test for building on Alpine Linux / Musl ...

Hopefully this will prevent any regression w.r.t. Musl.

CI: Temporarily disable LDC master ...

Until the support for preview=in is fixed.

CI: Use v2.100.2 temporarily instead of latest (2.101) ...

Because 2.101 is broken with preview=in, and dub relies on it.

CI: Add some more compiler to the test suite

CI: Upgrade Ubuntu to 20.04, actions/checkout to v3

Revert "Temporarily disable ldc-master as the dustmite test is broken" ...

This partially reverts commit b1f3b03.

Temporarily disable ldc-master as the dustmite test is broken

CI: Switch to macOS-11 as 10.15 will be removed Aug 30th ...

We've just been hit by a brownout.

Fail fast on Windows. ...

Ref https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#exit-codes-and-error-action-preference

use dlang-community/setup-dlang ...

setup-dlang was moved to dlang-community

Run run-unittest.d in Github Actions

Bump FRONTEND, move dmd to latest by default. (#2104) ...

* Update main.yml

* Update main.yml

Renaming a file ...

to conform to other file names.

Fix #2051 "Running unittests from dub single file packages fails" (#2052) ...

Performing test command dub imports every source file as module to build the project excluding the main source file. But this excluding may fail and in this case dub try to import the main source file as module. Single file package building fails because the main source file does not belong to any import path. Now both the current file and the main source file paths are compared in relative form to prevent importing the main source file as module.