AGENTS.md: do not insist on clang-tidy

clang-tidy is extremely finicky and requires an exact version in order to work,
and fails otherwise. When that happens the bots go crazy and try to do the most
stupid things to try and get a version compatible with the config. Reword the
rule so that hopefully they stop doing that.

AGENTS.md

@@ -49,8 +49,9 @@ display. This is critical for diagnosing build and test failures.
 
 ## clang-tidy
 
-- After changing C code, always run clang-tidy for the affected code and fix every finding before
-committing. CI runs the same checks and fails on any warning.
+- After changing C code, try to run clang-tidy for the affected code and fix every finding before
+committing, if a compatible version is already available (skip it if not, never try to obtain a new version yourself).
+CI runs the same checks and fails on any warning.
 - meson.build defines a test named `clang-tidy-<file name>` for every `.c` and `.h` file in its `sources`
 list. The `.h` file with the same name next to a `.c` file in the list gets a test as well. Other files
 have no test of their own, for example `src/basic/macro.h` and the sources of NSS and PAM modules.