[docs] Fix typo in llvm.experimental.vector.compress code-block snippet

Author: RKSimon

llvm/docs/LangRef.rst

@@ -19754,7 +19754,7 @@ This is an overloaded intrinsic. A number of scalar values of integer, floating
 from an input vector and placed adjacently within the result vector. A mask defines which elements to collect from the vector.
 The remaining lanes are filled with values from ``passthru``.
 
-:: code-block:: llvm
+.. code-block:: llvm
 
       declare <8 x i32> @llvm.experimental.vector.compress.v8i32(<8 x i32> <value>, <8 x i1> <mask>, <8 x i32> <passthru>)
       declare <16 x float> @llvm.experimental.vector.compress.v16f32(<16 x float> <value>, <16 x i1> <mask>, <16 x float> undef)