[MLIR][Presburger] Fix a comment in the unittests

[arjunp]

Hi, thanks for this patch.

Usually, we prepend patches in the MLIR Presburger library with [MLIR][Presburger]. Can you also edit the title to just reflect what the patch is doing, i.e., fixing a comment in the unittests. It's not necessary to mention that this is your first patch. :)

You can also mention in the summary that the comment is in the unittests. Please use full grammar in the summary, i.e. put a full stop at the end of your sentence.

mlir/unittests/Analysis/Presburger/PresburgerSetTest.cpp

TEST(SetTest, divisions) {
   // even multiples of 3 = multiples of 6.
   expectEqual(multiples3.intersect(evens), multiples6);
 
   PresburgerSet setA{parsePoly("(x) : (-x >= 0)")};
   PresburgerSet setB{parsePoly("(x) : (x floordiv 2 - 4 >= 0)")};
   EXPECT_TRUE(setA.subtract(setB).isEqual(setA));
 }
 
-/// Coalesce `set` and check that the `newSet` is equal to `set and that
+/// Coalesce `set` and check that the `newSet` is equal to `set` and that
 /// `expectedNumPoly` matches the number of Poly in the coalesced set.
-/// If one of the two
 void expectCoalesce(size_t expectedNumPoly, const PresburgerSet &set) {
   PresburgerSet newSet = set.coalesce();
   EXPECT_TRUE(set.isEqual(newSet));
   EXPECT_TRUE(expectedNumPoly == newSet.getNumDisjuncts());
 }
 
 TEST(SetTest, coalesceNoPoly) {
   PresburgerSet set = makeSetFromPoly(0, {});