CI: Pre-v9.0.0110 versions generate bogus documentation tag entries

Problem:  CI: Pre-v9.0.0110 versions generate bogus documentation tag
          entries
Solution: Set $VIMPROG to the freshly compiled Vim (Aliaksei Budavei)

related: #10813
related: #15099

Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/Makefile b/runtime/doc/Makefile
index 5f0786d..9cb38aa 100644
--- a/runtime/doc/Makefile
+++ b/runtime/doc/Makefile
@@ -7,7 +7,7 @@
 AWK = awk
 
 # Set to $(VIMTARGET) when executed from src/Makefile.
-VIMPROG = vim
+VIMPROG = ../../src/vim
 
 # include the config.mk from the source directory.  It's only needed to set
 # AWK, used for "make html".  Comment this out if the include gives problems.