Fix reference formatting in irradiance.py and pvsystem.py

- Remove non-standard double URL in AM1.5 spectra reference
- Remove "Pre-print:" prefix from Marion 2008 reference URL

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jason-curtis

pvlib/pvsystem.py

@@ -2084,7 +2084,7 @@ def retrieve_sam(name=None, path=None):
     Notes
     -----
     Files available at
-        https://github.com/NREL/SAM/tree/develop/deploy/libraries
+        https://github.com/NatLabRockies/SAM/tree/develop/deploy/libraries
 
     Examples
     --------
@@ -2963,7 +2963,7 @@ def pvwatts_dc(effective_irradiance, temp_cell, pdc0, gamma_pdc, temp_ref=25.,
        Module Performance," In Proc. 33rd IEEE Photovoltaic Specialists
        Conference (PVSC), San Diego, CA, USA, 2008, pp. 1-6,
        :doi:`10.1109/PVSC.2008.4922586`.
-       Pre-print: https://docs.nlr.gov/docs/fy08osti/42511.pdf
+       https://docs.nlr.gov/docs/fy08osti/42511.pdf
     """  # noqa: E501
 
     pdc = (effective_irradiance * 0.001 * pdc0 *

pvlib/spectrum/irradiance.py

@@ -78,7 +78,7 @@ def get_reference_spectra(wavelengths=None, standard="ASTM G173-03"):
     ----------
     .. [1] ASTM "G173-03 Standard Tables for Reference Solar Spectral
        Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface."
-    .. [2] “Reference Air Mass 1.5 Spectra,” www.nlr.gov.
+    .. [2] “Reference Air Mass 1.5 Spectra.” NLR.
        https://www.nlr.gov/grid/solar-resource/spectra-am1.5.html
     """  # Contributed by Echedey Luis, inspired by Anton Driesse (get_am15g)
     SPECTRA_FILES = {