Update unstable download URL in CI

[djhoese]

The old URL doesn't seem to have newest pandas and is having some download/HTTPS issues.

• Closes #xxxx
• Tests added
• Fully documented
• Add your name to AUTHORS.md if not there already

[codecov]

Codecov Report

Merging #2527 (f8f6dd6) into main (17006a8) will decrease coverage by 0.01%.
The diff coverage is 91.30%.

@@            Coverage Diff             @@
##             main    #2527      +/-   ##
==========================================
- Coverage   94.89%   94.89%   -0.01%     
==========================================
  Files         349      349              
  Lines       50842    50859      +17     
==========================================
+ Hits        48248    48263      +15     
- Misses       2594     2596       +2     

Flag	Coverage Δ
behaviourtests	4.32% <0.00%> (-0.01%)	⬇️
unittests	95.50% <91.30%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...sts/reader_tests/gms/test_gms5_vissr_navigation.py	99.29% <85.71%> (-0.71%)	⬇️
...atpy/tests/reader_tests/gms/test_gms5_vissr_l1b.py	99.66% <88.88%> (-0.34%)	⬇️
satpy/tests/reader_tests/utils.py	100.00% <100.00%> (ø)

[coveralls]

Pull Request Test Coverage Report for Build 5487925476

• 21 of 23 (91.3%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.002%) to 95.45%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
satpy/tests/reader_tests/gms/test_gms5_vissr_l1b.py	8	9	88.89%
satpy/tests/reader_tests/gms/test_gms5_vissr_navigation.py	6	7	85.71%

Totals
Change from base Build 5457841578:	-0.002%
Covered Lines:	48376
Relevant Lines:	50682

---

💛 - Coveralls

[sfinkens]

LGTM, thanks for fixing this!

[mraspaud]

Looks good, thanks for the fix. A couple of comments