test: fix expectations for bug-252 test (extraneous vertical space)

It's harder to say how it relates to sile-typesetter#1647, but checking with
-d all, this test showed a small vertical space at the bottom of
page 3, meaning the content frame was not stretched as much as
expected. It seems to be some lineskip. Now the text seems fully
stretched within the content frame.

tests/bug-252.expected

@@ -626,10 +626,10 @@ T	72 79 76 87 85 w=17.4414	(elitr)
 Mx 	166.7152
 T	86 72 71 w=13.6816	(sed)
 Mx 	17.4104
-My 	54.4238
+My 	54.5749
 T	71 76 68 80 w=20.5322	(diam)
 Mx 	37.4104
-My 	67.0827
+My 	67.5359
 T	55 75 76 86 w=17.5977	(This)
 Mx 	58.1245
 T	76 86 w=6.5723	(is)
@@ -638,11 +638,11 @@ T	68 w=4.5898	(a)
 Mx 	75.5194
 T	87 72 86 87 w=15.3662	(test)
 Mx 	90.8856
-My 	63.9040
+My 	64.3572
 Set font 	Gentium Plus;6.81152;400;;normal;;;LTR
 T	20 26 w=6.3925	(17)
 Mx 	97.2781
-My 	67.0827
+My 	67.5359
 Set font 	Gentium Plus;10;400;;normal;;;LTR
 T	17 w=2.2900	(.)
 Mx 	102.6845
@@ -652,7 +652,7 @@ T	76 83 86 88 80 w=25.2002	(ipsum)
 Mx 	158.4681
 T	71 82 79 82 85 w=21.9287	(dolor)
 Mx 	17.4104
-My 	79.4121
+My 	80.0165
 T	86 76 87 w=10.0146	(sit)
 Mx 	30.2264
 T	68 80 72 87 w=20.6836	(amet)
@@ -665,7 +665,7 @@ T	72 79 76 87 85 w=17.4414	(elitr)
 Mx 	166.7152
 T	86 72 71 w=13.6816	(sed)
 Mx 	17.4104
-My 	91.7416
+My 	92.4970
 T	71 76 68 80 w=20.5322	(diam)
 Mx 	41.1599
 T	81 82 81 88 80 92 w=34.3262	(nonumy)
@@ -676,7 +676,7 @@ T	87 72 80 83 82 85 w=30.3809	(tempor)
 Mx 	145.0697
 T	76 81 89 76 71 88 81 87 w=35.3271	(invidunt)
 Mx 	17.4104
-My 	104.0710
+My 	104.9775
 T	88 87 w=8.7402	(ut)
 Mx 	28.0592
 T	79 68 69 82 85 72 w=25.9863	(labore)
@@ -691,7 +691,7 @@ T	68 79 76 84 88 92 68 80 w=38.0127	(aliquyam)
 Mx 	163.8176
 T	72 85 68 87 w=16.6113	(erat)
 Mx 	17.4104
-My 	116.4005
+My 	117.4581
 T	86 72 71 w=13.6816	(sed)
 Mx 	34.2398
 T	71 76 68 80 w=20.5322	(diam)
@@ -712,7 +712,7 @@ T	70 88 w=9.6680	(cu)
 Mx 	177.0277
 T	16 w=3.3691	(-)
 Mx 	17.4104
-My 	128.7299
+My 	129.9386
 T	86 68 80 w=16.4844	(sam)
 Mx 	37.8984
 T	72 87 w=8.0615	(et)
@@ -729,7 +729,7 @@ T	72 68 w=9.2090	(ea)
 Mx 	153.4095
 T	85 72 69 88 80 w=26.9873	(rebum)
 Mx 	17.4104
-My 	141.0594
+My 	142.4191
 T	86 87 72 87 w=15.3662	(stet)
 Mx 	37.0854
 T	70 79 76 87 68 w=17.8223	(clita)
@@ -748,7 +748,7 @@ T	78 76 w=7.5879	(ki)
 Mx 	177.0277
 T	16 w=3.3691	(-)
 Mx 	17.4104
-My 	153.3888
+My 	154.8997
 T	80 68 87 68 w=20.6543	(mata)
 Mx 	41.0600
 T	86 68 81 70 87 88 86 w=30.9424	(sanctus)
@@ -763,7 +763,7 @@ T	71 82 79 82 85 w=21.9287	(dolor)
 Mx 	170.3822
 T	86 76 87 w=10.0146	(sit)
 Mx 	17.4104
-My 	165.7183
+My 	167.3802
 T	68 80 72 87 w=20.6836	(amet)
 Mx 	40.3202
 T	79 82 85 72 80 w=24.3506	(lorem)
@@ -782,7 +782,7 @@ T	86 72 w=8.4814	(se)
 Mx 	177.0277
 T	16 w=3.3691	(-)
 Mx 	17.4104
-My 	178.0477
+My 	179.8607
 T	87 72 w=8.0615	(te)
 Mx 	25.4719
 T	87 88 85 w=12.7002	(tur)
@@ -797,7 +797,7 @@ T	71 76 68 80 w=20.5322	(diam)
 Mx 	146.0707
 T	81 82 81 88 80 92 w=34.3262	(nonumy)
 Mx 	17.4104
-My 	190.3772
+My 	192.3413
 T	72 76 85 80 82 71 w=29.5508	(eirmod)
 Mx 	48.8697
 T	87 72 80 83 82 85 w=30.3809	(tempor)
@@ -814,7 +814,7 @@ T	71 82 w=10.2295	(do)
 Mx 	177.1379
 T	16 w=3.3691	(-)
 Mx 	17.4104
-My 	202.7066
+My 	204.8218
 T	79 82 85 72 w=16.3184	(lore)
 Mx 	36.5442
 T	80 68 74 81 68 w=27.6074	(magna)
@@ -831,7 +831,7 @@ T	89 82 w=9.9609	(vo)
 Mx 	177.0277
 T	16 w=3.3691	(-)
 Mx 	17.4104
-My 	215.0361
+My 	217.3023
 T	79 88 83 w=13.3057	(lup)
 Mx 	30.7161
 T	87 88 68 w=13.3301	(tua)
@@ -850,7 +850,7 @@ T	72 87 w=8.0615	(et)
 Mx 	160.1771
 T	77 88 86 87 82 w=20.2197	(justo)
 Mx 	17.4104
-My 	227.3655
+My 	229.7829
 T	71 88 82 w=15.5273	(duo)
 Mx 	35.9481
 T	71 82 79 82 85 72 86 w=30.4102	(dolores)