Don't fail build when symbols can't be uploaded (PR #11433)

Failing to upload symbols to Mozilla should not cause our build to fail.
The symbols are already saved as artefacts, if the upload to Mozilla
fails, it can be fixed manually.

Make the attempt more robust by trying multiple times with a short wait
in between.

appveyor.yml

@@ -140,7 +140,7 @@ before_test:
       $installerProcess | wait-process -Timeout 180
       $errorCode=$installerProcess.ExitCode
      } catch {
-      echo NVDA installer process timed out
+      echo "NVDA installer process timed out"
       $errorCode=1
       Add-AppveyorMessage "Unable to install NVDA prior to tests."
      }
@@ -253,9 +253,15 @@ deploy_script:
        artifacts=$artifacts
       }
       ConvertTo-Json -InputObject $data -Compress | ssh nvaccess@exbi.nvaccess.org nvdaAppveyorHook
+
       # Upload symbols to Mozilla.
       py -m pip install --no-warn-script-location requests
-       py appveyor\mozillaSyms.py
+      py appveyor\mozillaSyms.py
+      if($LastExitCode -ne 0) {
+        $errorCode=$LastExitCode
+        echo "Unable to upload symbols to Mozilla"
+        Add-AppveyorMessage "Unable to upload symbols to Mozilla"
+      }
      }
 
 on_finish:

appveyor/mozillaSyms.py

@@ -80,13 +80,33 @@ def generate():
 			count += 1
 	print('Added %d files to %s' % (count, ZIP_FILE))
 
+
 def upload():
-	r = requests.post(URL,
-		files={'symbols.zip': open(ZIP_FILE, 'rb')},
-		headers={'Auth-Token': os.getenv('mozillaSymsAuthToken')},
-		allow_redirects=False
-	)
-	if r.status_code >= 200 and r.status_code < 300:
+	errors = []  # capture errors, to report if all attempts fail.
+	for i in range(7):
+		if i > 0:
+			print("Sleeping for 15 seconds before next attempt.")
+			import time
+			time.sleep(15)
+		try:
+			r = requests.post(
+				URL,
+				files={'symbols.zip': open(ZIP_FILE, 'rb')},
+				headers={'Auth-Token': os.getenv('mozillaSymsAuthToken')},
+				allow_redirects=False
+			)
+			break  # success
+		except Exception as e:
+			print(f"Attempt {i + 1} failed: {e!r}")
+			errors.append(repr(e))
+	else:  # no break in for loop
+		allErrors = "\n".join(
+			f"Attempt {index + 1} error: \n{e}"
+			for index, e in enumerate(errors)
+		)
+		raise RuntimeError(allErrors)
+
+	if 200 <= r.status_code < 300:
 		print('Uploaded successfully!')
 	elif r.status_code < 400:
 		print('Error: bad auth token? (%d)' % r.status_code)