org-test: Fix ERC errors using latest Emacs master

* testing/lisp/test-ob-C.el:
* testing/lisp/test-ob-awk.el:
* testing/lisp/test-ob-sed.el: Add missing provide.
* testing/lisp/test-property-inheritance.el: Fix incorrect feature
name.
* testing/org-test.el (org-test-load): Use `require' instead of
`load-file' to load tests.  `load-file' can lead to duplicate test
definitions that now trigger ERC errors.

See https://lists.gnu.org/archive/html/bug-gnu-emacs/2021-11/msg01968.html

testing/lisp/test-ob-C.el

@@ -183,4 +183,5 @@
 				 ("Friday" "friday"))
 			       (org-babel-execute-src-block))))))
 
+(provide 'test-ob-C)
 ;;; test-ob-C.el ends here

testing/lisp/test-ob-awk.el

@@ -46,3 +46,6 @@
   (org-test-at-id "9e998b2a-3581-43fe-b26d-07d3c507b86a"
     (org-babel-next-src-block 4)
     (should (equal '(("a" "b" "c")) (org-babel-execute-src-block)))))
+
+(provide 'test-ob-awk)
+;;; test-ob-awk.el ends here

testing/lisp/test-ob-sed.el

@@ -58,5 +58,5 @@
 			 (buffer-string)))))))
 
 
-
+(provide 'test-ob-sed)
 ;;; test-ob-sed ends here

testing/lisp/test-property-inheritance.el

@@ -45,6 +45,5 @@
    (org-babel-next-src-block 3)
    (should (= 6 (org-babel-execute-src-block)))))
 
-(provide 'test-ob-R)
-
+(provide 'test-property-inheritance)
 ;;; test-property-inheritance.el ends here

testing/org-test.el

@@ -373,7 +373,11 @@ setting `pp-escape-newlines' to nil manually."
 		   (condition-case err
 		       (when (string-match "^[A-Za-z].*\\.el$"
 					   (file-name-nondirectory path))
-			 (load-file path))
+                         (let ((feature-name
+                                (intern
+                                 (file-name-base
+                                  (file-name-nondirectory path)))))
+			   (require feature-name path)))
 		     (missing-test-dependency
 		      (let ((name (intern
 				   (concat "org-missing-dependency/"