python-info-dedenter-opening-block-positions: Fix to support "bare" match

* lisp/progmodes/python.el
(python-info-dedenter-opening-block-positions): Make the check
stricter.  Require that block starts only at indentation.

* test/lisp/progmodes/python-tests.el
(python-indent-after-bare-match): Another test (bug#62031).

lisp/progmodes/python.el

@@ -5792,7 +5792,9 @@ likely an invalid python file."
             (while (python-nav--syntactically
                     (lambda ()
                       (cl-loop while (re-search-backward (python-rx block-start) nil t)
-                               if (memq (char-before) '(nil ?\s ?\t ?\n))
+                               if (save-match-data
+                                    (looking-back (rx line-start (* whitespace))
+                                                  (line-beginning-position)))
                                return t))
                     #'<)
               (let ((indentation (current-indentation)))

test/lisp/progmodes/python-tests.el

@@ -1994,6 +1994,20 @@ def test_re(string):
    (python-tests-look-at "else:")
    (should (= (python-indent-calculate-indentation) 4))))
 
+(ert-deftest python-indent-after-bare-match ()
+  "Test BUG 62031 regression."
+  (python-tests-with-temp-buffer
+   "
+from re import match
+
+def test_re(string):
+    if match('^[a-c]+$', string):
+        print('yes')
+    else:
+    "
+   (python-tests-look-at "else:")
+   (should (= (python-indent-calculate-indentation) 4))))
+
 
 ;;; Filling