Avoid re-using variable names in tests

[eerovaher]

I have annotated more pyerfa ufuncs as np.ufunc instances in my local repository, but the improved annotations are triggering type-checking errors in erfa/tests/test_ufunc.py. The errors are caused by code that looks like

astrom = erfa_ufunc...
astrom = astrom.view(np.recarray)

With the improved annotations type checkers can infer that the astrom in the first line is an array or an array scalar, but the result of the view() method is an np.recarray instance, which is incompatible with the inferred type of the variable. This PR solves the problem by avoiding two separate assignments to astrom where possible, or using a different variable name for the first astrom where two assignments are needed.

The full difference between `erfa/tests/test_ufunc.py` in current `main` and in this PR

106,107c106
<     astrom = erfa_ufunc.apcg(date1, date2, ebpv, ehp)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.apcg(date1, date2, ebpv, ehp).view(np.recarray)
134,135c133
<     astrom = erfa_ufunc.apcg13(date1, date2)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.apcg13(date1, date2).view(np.recarray)
176,177c174
<     astrom = erfa_ufunc.apci(date1, date2, ebpv, ehp, x, y, s)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.apci(date1, date2, ebpv, ehp, x, y, s).view(np.recarray)
204,205c201,202
<     astrom, eo = erfa_ufunc.apci13(date1, date2)
<     astrom = astrom.view(np.recarray)
---
>     astrom_raw, eo = erfa_ufunc.apci13(date1, date2)
>     astrom = astrom_raw.view(np.recarray)
256,257c253
<     astrom = erfa_ufunc.apco(date1, date2, ebpv, ehp, x, y, s, theta, elong, phi, hm, xp, yp, sp, refa, refb)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.apco(date1, date2, ebpv, ehp, x, y, s, theta, elong, phi, hm, xp, yp, sp, refa, refb).view(np.recarray)
303,304c299,300
<     astrom, eo, j = erfa_ufunc.apco13(utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
<     astrom = astrom.view(np.recarray)
---
>     astrom_raw, eo, j = erfa_ufunc.apco13(utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
>     astrom = astrom_raw.view(np.recarray)
360,361c356
<     astrom = erfa_ufunc.apcs(date1, date2, pv, ebpv, ehp)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.apcs(date1, date2, pv, ebpv, ehp).view(np.recarray)
395,396c390
<     astrom = erfa_ufunc.apcs13(date1, date2, pv)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.apcs13(date1, date2, pv).view(np.recarray)
424,425c418
<     astrom = erfa_ufunc.aper(theta, astrom)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.aper(theta, astrom).view(np.recarray)
434,435c427
<     astrom = erfa_ufunc.aper13(ut11, ut12, astrom)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.aper13(ut11, ut12, astrom).view(np.recarray)
449,450c441
<     astrom = erfa_ufunc.apio(sp, theta, elong, phi, hm, xp, yp, refa, refb)
<     astrom = astrom.view(np.recarray)
---
>     astrom = erfa_ufunc.apio(sp, theta, elong, phi, hm, xp, yp, refa, refb).view(np.recarray)
475,476c466,467
<     astrom, j = erfa_ufunc.apio13(utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
<     astrom = astrom.view(np.recarray)
---
>     astrom_raw, j = erfa_ufunc.apio13(utc1, utc2, dut1, elong, phi, hm, xp, yp, phpa, tc, rh, wl)
>     astrom = astrom_raw.view(np.recarray)