ob-core: Fix handling of multiple noweb refs in same line

* lisp/ob-core.el (org-babel-expand-noweb-references): Don't anchor
noweb regexp at start of line to allow multiple matches per line.
* testing/lisp/test-ob-tangle.el (ob-tangle/multiple-noweb-in-line):
Add test.

This fixes a regression introduced by c1aed9f80 (ob-core: Refactor
`org-babel-expand-noweb-references', 2020-01-12), which was part of
the 9.4 release.

Reported-by: Tom Gillespie <tgbugs@gmail.com>
Ref: https://orgmode.org/list/CA+G3_PO2yO1jMMpdrkc39BGQQ2eU5X4FzTEJVotjDJo-50dsqQ@mail.gmail.com

lisp/ob-core.el

@@ -2781,7 +2781,7 @@ block but are passed literally to the \"example-block\"."
          (lang (nth 0 info))
          (body (nth 1 info))
 	 (comment (string= "noweb" (cdr (assq :comments (nth 2 info)))))
-	 (noweb-re (format "^\\(.*?\\)\\(%s\\)"
+	 (noweb-re (format "\\(.*?\\)\\(%s\\)"
 			   (with-current-buffer parent-buffer
 			     (org-babel-noweb-wrap))))
 	 (cache nil)

testing/lisp/test-ob-tangle.el

@@ -420,6 +420,38 @@ another block
 		    (org-split-string (buffer-string))))
 	      (delete-file file))))))
 
+(ert-deftest ob-tangle/multiple-noweb-in-line ()
+  "Test handling of multiple noweb references in a single line."
+  (should
+   (equal '("1" "2" "1")
+	  (let ((file (make-temp-file "org-tangle-")))
+	    (unwind-protect
+		(progn
+		  (org-test-with-temp-text-in-file
+		      (format "
+#+name: block1
+#+begin_src elisp
+1
+#+end_src
+
+#+name: block2
+#+begin_src elisp
+2
+#+end_src
+
+#+name: block3
+#+begin_src elisp :noweb yes :tangle %s
+<<block1>> <<block2>> <<block1>>
+#+end_src"
+			      file)
+		    (let ((org-babel-noweb-error-all-langs nil)
+			  (org-babel-noweb-error-langs nil))
+		      (org-babel-tangle)))
+		  (with-temp-buffer
+		    (insert-file-contents file)
+		    (org-split-string (buffer-string))))
+	      (delete-file file))))))
+
 (ert-deftest ob-tangle/detangle-false-positive ()
   "Test handling of false positive link during detangle."
   (let (buffer)