Fix warnings about non-externalized string literals

Four occurrences in RefSpec marked with //$NON-NLS-<n>$.

Change-Id: Ie603a58c41357562f0739445e3fe77ca87a3eb54
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefSpec.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefSpec.java
index e36eecc..61d1935 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefSpec.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/RefSpec.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008, 2013 Shawn O. Pearce <spearce@spearce.org> and others
+ * Copyright (C) 2008, 2022 Shawn O. Pearce <spearce@spearce.org> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -154,7 +154,7 @@
 		this.allowMismatchedWildcards = mode;
 		String s = spec;
 
-		if (s.startsWith("^+") || s.startsWith("+^")) {
+		if (s.startsWith("^+") || s.startsWith("+^")) { //$NON-NLS-1$ //$NON-NLS-2$
 			throw new IllegalArgumentException(
 					JGitText.get().invalidNegativeAndForce);
 		}
@@ -164,7 +164,7 @@
 			s = s.substring(1);
 		}
 
-		if(s.startsWith("^")) {
+		if (s.startsWith("^")) { //$NON-NLS-1$
 			negative = true;
 			s = s.substring(1);
 		}
@@ -251,7 +251,7 @@
 	 *             the specification is invalid.
 	 */
 	public RefSpec(String spec) {
-		this(spec, spec.startsWith("^") ? WildcardMode.ALLOW_MISMATCH
+		this(spec, spec.startsWith("^") ? WildcardMode.ALLOW_MISMATCH //$NON-NLS-1$
 				: WildcardMode.REQUIRE_MATCH);
 	}