fixup: reword based on review comments

Author: gireeshpunathil

doc/contributing/diagnostic-tooling-support-tiers.md

@@ -43,10 +43,9 @@ the following tiers.
     organization or website;
   * The tool must be open source.
 
-* Tier 3 - Its test suite will be run either as nightly in Node.js CI
-  or in CITGM (in case if a test cannot be configured and run in nightly
-  by virtue of the nature of the tool in question) and issues opened for
-  failures. Does not block shipping a release.
+* Tier 3 - If possible its test suite will be run at least nightly
+  in the Node.js CI or in CITGM, and issues opened for failures.
+  Does not block shipping a release.
 
 * Tier 4 - Does not block shipping a release.