JP-3643: Add background error propagation for non-IFU spectral extraction

CHANGES.rst

@@ -89,6 +89,9 @@ extract_1d
 - Add propagation of uncertainty when annular backgrounds are subtracted
   from source spectra during IFU spectral extraction. [#8515]
 
+- Add propagation of background uncertainty when background is subtracted from 
+  source spectra during non-IFU spectral extraction. [#8532]
+
 - Fix error in application of aperture correction to variance arrays. [#8530]
 
 extract_2d

jwst/extract_1d/extract1d.py

@@ -457,6 +457,11 @@ def _extract_src_flux(image, var_poisson, var_rnoise, var_flat, x, j, lam, srcli
     # subtract background per pixel:
     val -= bkg
 
+    # add background variance to variance in source extraction region
+    f_var_poisson += b_var_poisson
+    f_var_rnoise += b_var_rnoise
+    f_var_flat += b_var_flat
+
     # scale per pixel values by pixel area included in extraction
     val *= area
     bkg *= area