get docs building with goi 1.66+

It builds now, but some doc sections are missing. Fix this properly in
8.11.

See https://github.com/libvips/libvips/issues/1836

ChangeLog

@@ -10,6 +10,7 @@
 - better heif signature detection [lovell]
 - fix vips_fractsurf() typo [kleisauke]
 - better heif EOF detection [lovell]
+- fix gir build with g-o-i 1.66+ [László]
 
 9/8/20 started 8.10.1
 - fix markdown -> xml conversion in doc generation

libvips/iofuncs/error.c

@@ -71,7 +71,7 @@
 #endif /*OS_WIN32*/
 
 /**
- * SECTION: error
+ * SECTION: errors
  * @short_description: error messages and error handling
  * @stability: Stable
  * @include: vips/vips.h

libvips/iofuncs/rect.c

@@ -45,7 +45,7 @@
 #include <vips/vips.h>
 
 /**
- * SECTION: rect
+ * SECTION: rectangle
  * @short_description: the VIPS rectangle class
  * @stability: Stable
  * @see_also: <link linkend="VipsRegion">region</link>

libvips/resample/interpolate.c

@@ -63,7 +63,7 @@
 #include <vips/internal.h>
 
 /**
- * SECTION: interpolate
+ * SECTION: interpolator
  * @short_description: various interpolators: nearest, bilinear, and
  * some non-linear
  * @stability: Stable