Update src/doc/unstable-book/src/language-features/re-rebalance-coherence.md

Co-Authored-By: weiznich <Georg_semmler_05@web.de>

Author: varkor

src/doc/unstable-book/src/language-features/re-rebalance-coherence.md

@@ -6,7 +6,7 @@ The tracking issue for this feature is: [#55437]
 
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-The `re_rebalance_coherence` feature tweaks the rules which trait
+The `re_rebalance_coherence` feature tweaks the rules regarding which trait
 impls are allowed in crates.
 The following rule is used: