Fix variant float8 expected files to have exactly the expected spacing.

This wasn't important when we used diff's -w (--ignore-all-space) option
to compare regression result files, but it is now.  Per buildfarm member
canary, which evidently has been offline since we did that in November,
but came to life again today.

src/test/regress/expected/float8-small-is-zero.out

@@ -19,13 +19,13 @@ LINE 1: SELECT '-10e400'::float8;
 SELECT '10e-400'::float8;
  float8 
 --------
-     0
+      0
 (1 row)
 
 SELECT '-10e-400'::float8;
  float8 
 --------
-    -0
+     -0
 (1 row)
 
 -- bad input

src/test/regress/expected/float8-small-is-zero_1.out

@@ -19,13 +19,13 @@ LINE 1: SELECT '-10e400'::float8;
 SELECT '10e-400'::float8;
  float8 
 --------
-     0
+      0
 (1 row)
 
 SELECT '-10e-400'::float8;
  float8 
 --------
-     0
+      0
 (1 row)
 
 -- bad input