BUG: Fix incorrect brackets in cephes hyperg.h

[steppi]

Reference issue

This is fixes one of the warnings mentioned in #20740, but would not be sufficient to close that issue.

What does this implement/fix?

This PR fixes some incorrect bracketing in hy1f1a in scipy/special/special/cephes/hyperg.h. While translating cephes into C++, in some places I added brackets in one line if blocks which omitted them, but in this case I added the opening bracket but not the closing bracket. I've simply removed this extraneous opening bracket to bring the code to it's original state.

Additional information

The cephes implementation of hyp1f1 is not well tested because we use Boost for the hyp1f1 ufunc. The cephes hyp1f1 is only used in orthogonal_eval.pxd in the function eval_genlaguerre. I briefly tried to find a test case for eval_genlaguerre which would hit the control path without a return value, but couldn't find one. I think it's fine not to include a test case; one can compare this PR to the original cephes code.

scipy/scipy/special/cephes/hyperg.c

Lines 237 to 247 in f133c27

	if (asum == INFINITY || asum == -INFINITY)
	/* infinity */
	acanc = 0;
	acanc *= 30.0; /* fudge factor, since error of asymptotic formula
	* often seems this much larger than advertised */
	adone:
	*err = acanc;
	return (asum);
	}

Thanks @fancidev for bringing this to our attention in #20740