dist/tools: update doc of can_fast_ci_run.py and add VERSION file to fast-run list

[crasbe]

Contribution description

The documentation for the classify_changes function was outdated, so I updated it.

Also, the addition of a VERSION file should probably not cause a full build?
I don't think our build system even uses the file, RIOT derives it's version from the GIT_VERSION

Testing procedure

Clone a fresh copy of the mothership git clone https://github.com/RIOT-OS/RIOT, checkout the 2026.04-branch, checkout the #22244 PR (I use gh pr checkout 22244, you can use something else too I guess?), run the following command:

buechse@skyleaf:~/RIOTstuff/riot-upstream$ gh repo clone RIOT-OS/RIOT
Cloning into 'RIOT'...
remote: Enumerating objects: 401023, done.
remote: Counting objects: 100% (191/191), done.
remote: Compressing objects: 100% (145/145), done.
remote: Total 401023 (delta 106), reused 53 (delta 44), pack-reused 400832 (from 2)
Receiving objects: 100% (401023/401023), 177.40 MiB | 39.73 MiB/s, done.
Resolving deltas: 100% (276472/276472), done.
Updating files: 100% (15811/15811), done.

buechse@skyleaf:~/RIOTstuff/riot-upstream$ cd RIOT/

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ git checkout 2026.04-branch
branch '2026.04-branch' set up to track 'origin/2026.04-branch'.
Switched to a new branch '2026.04-branch'

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ gh pr checkout 22244
From https://github.com/RIOT-OS/RIOT
 * [new ref]               refs/pull/22244/head -> final_release_pr
Switched to branch 'final_release_pr'

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ dist/tools/ci/can_fast_ci_run.py --upstreambranch 2026.04-branch --explain --debug
Couldn't classify changes: File "VERSION" doesn't match any known category

Checkout this PR in the same repository, checkout final_release_pr again, cherry pick this PR (and the other changes to can_fast_ci_run.py) onto it and run the command again.

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ gh pr checkout 22247
remote: Enumerating objects: 17, done.
remote: Counting objects: 100% (17/17), done.
remote: Compressing objects: 100% (2/2), done.
remote: Total 12 (delta 10), reused 12 (delta 10), pack-reused 0 (from 0)
Unpacking objects: 100% (12/12), 1024 bytes | 341.00 KiB/s, done.
From https://github.com/RIOT-OS/RIOT
 * [new ref]               refs/pull/22247/head -> pr/VERSION_fast_run
Switched to branch 'pr/VERSION_fast_run'

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ git checkout final_release_pr
Switched to branch 'final_release_pr'

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ git cherry-pick 8d6b1ba f5e327d0c9 b6d632467e 2fd4ffe8da
[final_release_pr 134591029b] dist/tools/ci: update classification
 Author: Marian Buschsieweke <marian.buschsieweke@ml-pa.com>
 Date: Fri Apr 17 13:06:23 2026 +0200
 1 file changed, 2 insertions(+), 2 deletions(-)
[final_release_pr 75357673c1] dist/tools: add GitHub workflows to can_fast_ci_run
 Date: Tue May 5 17:18:16 2026 +0200
 1 file changed, 2 insertions(+), 1 deletion(-)
[final_release_pr fe7ee53cb5] dist/tools: fix documentation of can_fast_ci_run.py
 Date: Wed May 6 13:59:04 2026 +0200
 1 file changed, 2 insertions(+), 4 deletions(-)
[final_release_pr ec4c54cf41] dist/tools: add VERSION file as fast-runnable to can_fast_ci_run.py
 Date: Wed May 6 13:59:59 2026 +0200
 1 file changed, 1 insertion(+), 1 deletion(-)

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ dist/tools/ci/can_fast_ci_run.py --upstreambranch 2026.04-branch --explain --debug
Other
=====

doc
---

- VERSION
- release-notes.txt

tools
-----

- dist/tools/ci/can_fast_ci_run.py

buechse@skyleaf:~/RIOTstuff/riot-upstream/RIOT$ echo $?
0

Issues/PRs references

Noticed in #22244.

Declaration of AI-Tools / LLMs usage:

AI-Tools / LLMs that were used are:

• none

[crasbe]

Updated the testing description so now it actually works :)

[AnnsAnns]

Sounds good 🙈

[AnnsAnns]

I am gambling the CI workflow wont time out since the release merge queue is half done already

[crasbe]

I am gambling the CI workflow wont time out since the release merge queue is half done already

Hold my tflite-micro.

[riot-ci]

Murdock results

✔️ PASSED

2fd4ffe dist/tools: add VERSION file as fast-runnable to can_fast_ci_run.py

Success	Failures	Total	Runtime
1	0	1	01m:52s

Artifacts

• Documentation preview

[crasbe]

Thank you for the reviews :)