fix: split key_prefix validation into two separate validators

Per review by @deiga: use two StringMatch validators inside
validation.All() — one for allowed characters (^[a-zA-Z0-9.=+:/#_-]+$)
and one for the digit-suffix check (\D$) — instead of a single
combined regex. This makes the error messages more precise.

Author: LeC-D

github/resource_github_repository_autolink_reference.go

@@ -69,9 +69,15 @@ func resourceGithubRepositoryAutolinkReference() *schema.Resource {
 				Required:    true,
 				ForceNew:    true,
 				Description: "This prefix appended by a number will generate a link any time it is found in an issue, pull request, or commit",
-				ValidateDiagFunc: validation.ToDiagFunc(validation.StringMatch(
-					regexp.MustCompile(`^[a-zA-Z0-9.=+:/#_-]*[a-zA-Z.=+:/#_-]$`),
-					"must only contain letters, numbers, or .-_+=:/# and must not end with a number",
+				ValidateDiagFunc: validation.ToDiagFunc(validation.All(
+					validation.StringMatch(
+						regexp.MustCompile(`^[a-zA-Z0-9.=+:/#_-]+$`),
+						"must only contain letters, numbers, or the characters .-_+=:/#",
+					),
+					validation.StringMatch(
+						regexp.MustCompile(`\D$`),
+						"must not end with a number",
+					),
 				)),
 			},
 			"target_url_template": {