Hopefully, fix the long-standing problem with h2root

[couet]

Using the C option (meaning C I.O) in hropen seems to fix the issue on Mac.

[github-actions]

Test Results

    18 files      18 suites   4d 11h 9m 38s ⏱️
 2 682 tests  2 680 ✅ 0 💤 2 ❌
46 556 runs  46 553 ✅ 0 💤 3 ❌

For more details on these failures, see this check.

Results for commit e052758.

♻️ This comment has been updated with latest results.

[hahnjo]

As far as I can tell, this shouldn't make a difference because HROPEN defaults to to C unless F is specified:

root/misc/minicern/src/hbook.f

Lines 260 to 263 in 80023e0

	IF (INDEX(CHOPT,'F').EQ.0) THEN
	IC = MIN(LENOCC(CHOPT)+1,8)
	CHOPT(IC:IC) = 'C'
	ENDIF

[couet]

@hahnjo it made on on MacOS. (long debug)

[hahnjo]

my comment from #15915 (comment) still stands: based on the code, there should be no change in behavior because C is already the default.

[couet]

I know "c" is supposed to be the default, but this change made a difference on Mac when I debugged it a while ago. I guess it is worth merging.