Normalize focused goal output

Merge the "1 focused goal" line with the subsequent "(shelved: 1)" line,
since this is the new output in Coq 8.15+.

std++ does not currently produce this output, since no test calls `Show`
with shelved goals, but this future-proofs the test normalization.

test-normalizer.sed

 # adjust for https://github.com/coq/coq/pull/13656
 s/subgoal/goal/g
+# merge with subsequent line for https://github.com/coq/coq/pull/14999
+/[0-9]* focused goals\?$/{N;s/\n */ /;}